Incretin Drug: the next incretin drugs, one molecule at a time

Amycretin: One Molecule, Amylin and GLP-1

2026-11-01T00:00:00+00:00

One thing that happens when a drug class starts working is that everyone in it tries to fit more of the working parts into fewer molecules. The drug called amycretin is a tidy example. It is a single peptide built to activate the GLP-1 receptor (the target behind the current generation of weight-loss drugs) and the amylin receptor (the target of a second satiety hormone). In early trials it produced 13.1% weight loss at 12 weeks when taken by mouth and 24.3% weight loss over 36 weeks when injected under the skin.</p>

Those are the headline numbers, and they come from early studies of different lengths using different routes of administration, so they are not a scoreboard. What the available facts do not settle is just as important. They do not say when, or whether, it will be approved, and they do not give a phase 3 result. They also leave open something stranger: whether “amylin and GLP-1” is even a complete description of what the molecule does.</p>

What amycretin is, in plain terms</h2>
A review titled “Amycretin in obesity: Mechanisms, clinical efficacy, and …” describes it as a “unimolecular GLP-1 and amylin receptor agonist.” Translated: it is one chain of amino acids that turns on two kinds of appetite receptors. “Unimolecular” is doing all the work in that phrase. It means the two activities are not two drugs sharing a syringe. They are one drug that happens to fit two locks.</p>
This is the same design idea behind tirzepatide, which the site covers elsewhere and which one paper says earned the nickname “twincretin” (pharmacology has a weakness for portmanteaus). Tirzepatide hits GIP and GLP-1. Retatrutide hits GLP-1, GIP and glucagon. Amycretin swaps the gut-hormone partner for amylin, which is a pancreatic hormone that also tells the brain you are full. So the shape is familiar. Only the partner changes.</p>

Why not just mix two drugs together?</h2>
Here is the sensible reaction. If you want amylin activity and GLP-1 activity, you can take an amylin drug and a GLP-1 drug. That has already been done. CagriSema is, in the words of its sources, “a fixed-dose combination of semaglutide (a GLP-1 receptor agonist) and cagrilintide (an amylin analogue),” and in the REDEFINE 1 trial published in NEJM it produced 22.7% mean weight reduction at the 2.4 mg / 2.4 mg dose. Two well-characterized molecules, one injection, a big number. Why build a new hybrid when the mixture works?</p>
To be fair, that objection is basically correct as far as it goes. A combination lets you tune each half separately, and each half arrives with its own history. On the other hand, a single molecule has one manufacturing process, one set of pharmacokinetics (how the drug moves through and leaves the body) and one thing for regulators to evaluate, instead of two things plus their interaction. And it may be a more natural candidate for a pill, which is where this gets interesting. It is far from clear you can make two separate peptides survive the stomach together on the same schedule. Amycretin has oral data at all, which tells you someone thought one peptide was a more tractable oral problem than two.</p>
Everyone in this story is acting reasonably. The chemist wants one clean molecule because one molecule is easier to make and to study. The company wants a product that differs from its neighbors, because a crowded field rewards anything that does. The regulator wants to know what every active ingredient does, and fewer ingredients means fewer questions. I mean, nobody set out to make this more complicated.</p>
And yet it is.</p>

The third receptor nobody put in the name</h2>
The outlet Metabolic Care Today describes amycretin as “a unimolecular peptide agonist of GLP-1, amylin, AND calcitonin receptors,” capital letters theirs, and counts “three receptor targets.” So the drug marketed in conversation as an amylin/GLP-1 dual is, by at least one description, a triple. The calcitonin receptor sort of comes along for the ride.</p>
This is not unique to amycretin. Structure Therapeutics has an oral small molecule, ACCG-2671, described as a dual amylin and calcitonin receptor agonist (a “DACRA”) with high binding affinity at the calcitonin receptor and at an amylin receptor subtype called AMY3R. In obese rats it produced dose-dependent weight loss, with additive effects when combined with semaglutide. So amylin-side drug design seems to travel with calcitonin activity as a matter of course. Why those two keep showing up together is a receptor biology question, and the facts here do not explain it. I assume the medicinal chemists find this less surprising than I do.</p>
The naming, then, reflects what people care about rather than everything the molecule touches. That is common. It is also how you end up with a field whose drug names are a running count of receptors, plus a footnote.</p>

Reading the early oral and injectable amycretin data</h2>
The two numbers are 13.1% at 12 weeks orally and 24.3% over 36 weeks by subcutaneous injection. The tempting move is to compare them and conclude the injection is about twice as good. That is the wrong comparison. The injectable study ran three times as long, and weight loss on these drugs generally keeps accumulating over months, so a 12-week figure is a snapshot of something still moving. The facts available do not give doses, trial sizes, placebo arms or dropout rates for either study, so the honest position is that the oral figure is promising for a short trial, the injectable figure is large, and neither is a head-to-head result.</p>
For scale, and only for scale: tirzepatide produced 19.5% and 20.9% mean weight reduction at 10 mg and 15 mg in SURMOUNT-1, a phase 3 trial. A review in Annals of Internal Medicine pooling 26 randomized trials in 15,491 adults without diabetes put retatrutide at 24.2% at 12 mg weekly, ahead of tirzepatide (17.8%) and subcutaneous semaglutide (13.9%). Amycretin’s 24.3% sits right next to those numbers. But it comes from an earlier, smaller-looking evidence base, and cross-trial comparison is the thing everyone in this field agrees not to do and then does anyway (I am doing it right now, in a paragraph about not doing it).</p>
Here is an invented scenario, offered only to show where the logic leads. A program finds that two receptors beat one, so it adds a third. The third beats two, so someone in a meeting says, “Hey, what if we also hit the receptor for, like, feeling satisfied after a good sandwich?” Eventually there is one molecule that activates every satiety receptor in the body, and its name is an alphabet. It is the drug-design version of Everything Everywhere All at Once, and its development team needs a whiteboard the size of a tennis court. That is not where amycretin is. It is roughly where the incentive points.</p>

Where it sits in a crowded pipeline</h2>
One review identifies three main directions for next-generation incretin drugs: dual and triple receptor agonists, “biased agonist design,” and oral formulations. That last phrase means building a drug that switches on only some of a receptor’s signaling pathways rather than all of them. Amycretin touches two of the three directions at once. It is a multi-agonist, and it has an oral version.</p>
The oral lane is not empty, though. Orforglipron, Eli Lilly’s small-molecule (non-peptide) GLP-1 pill, is described as the first oral small-molecule GLP-1 agonist to successfully complete a phase 3 trial, and Lilly positions it as potentially the first oral GLP-1 approved specifically for obesity. Aleniglipron and HRS-7535 are other small-molecule oral GLP-1 agonists with published trial data. Those are small molecules aimed at one receptor. Amycretin is a peptide aimed at two or three. A 2024 systematic review counted 14 ongoing phase 3 obesity trials, including CagriSema, retatrutide, orforglipron, survodutide, mazdutide, etc. In that list, amycretin had no phase 3 entry.</p>
So the bet is specific. Amycretin’s developer is wagering that a single peptide carrying amylin activity can compete with a two-drug amylin combination on the injectable side and with GLP-1-only pills on the oral side. If it works, it is one molecule covering both markets. I would rather not think about what the marketing department has planned for that.</p>
What comes next is the part the facts leave blank: longer trials, larger trials, direct comparisons, and the tolerability data that decides whether a big number becomes a drug people stay on. All of that is still ahead. The early results establish that the design idea is not crazy. They do not establish that it wins.</p>
Eventually every weight-loss drug will be several weight-loss drugs.</p>

Amylin: The Other Satiety Hormone

2026-11-01T00:00:00+00:00

The most-watched obesity drug combinations right now take a GLP-1 drug, which already works quite well, and bolt on a second hormone that most people outside endocrinology have never heard of. That hormone is amylin. It is having a moment.</p>

Plainly: amylin is a satiety hormone, and drugs that act on amylin receptors are being paired with GLP-1 drugs or built into the same molecule as them. The leading examples are CagriSema, a combination product that produced 22.7% mean weight reduction in its REDEFINE 1 trial, published in NEJM, and amycretin, a single molecule that hit 24.3% weight loss over 36 weeks as an injection. A 2026 review describes amycretin’s mechanism as “synergistically engaging hindbrain-mediated satiety pathways and delaying gastric emptying to overcome metabolic plateaus.” That sentence is most of what the drug industry wants from amylin. The rest of this piece is about why.</p>

What amylin does, as far as drug developers care</h2>
There are two parts to that review’s description. The first is the hindbrain, the old back part of the brain that handles a lot of unglamorous bodily bookkeeping, including the feeling of having eaten enough. The second is gastric emptying, which is how fast your stomach passes food along.</p>
The gastric part works a bit like a restaurant kitchen that slows the pace of courses. If the main arrives forty minutes after the appetizer, a lot of people skip dessert, not out of virtue but because the appetizer has had time to register. Same food, different timing, less eating. (The kitchen is not trying to help you. It is just slow.)</p>
Amylin is not the only hormone in this business. GLP-1, according to structural work on its receptor, has “essential roles in regulating insulin secretion, carbohydrate metabolism, and appetite,” which is the line from the Cryo-EM paper that described the activated GLP-1 receptor. The point is that GLP-1 and amylin both touch appetite, but through receptors that are not the same receptor. That is what makes pairing them interesting rather than redundant.</p>
There is also a third receptor in the story. Metabolic Care Today describes amycretin as “a unimolecular peptide agonist of GLP-1, amylin, AND calcitonin receptors (three receptor targets).” The capital AND is theirs. Calcitonin receptors keep showing up next to amylin receptors in these programs, and the drugs are designed to hit both.</p>

The first amylin drug, and what these sources do not say</h2>
This is where I would normally tell you the founding story: who made the first amylin analog, when it was approved, how it sold, why it faded. I write about drug pipelines for a living, which mostly means reading the same three percentages in forty different press releases, and I would love to do the history part. But the source material behind this article does not document that history. So the dates, the sales, and the reasons it did not become a blockbuster are not settled here, and I am not going to make them up.</p>
What the sources do settle is that amylin analogs are back, in a pipeline that is very crowded. A 2024 systematic review found 14 ongoing phase 3 trials for obesity drugs, and CagriSema, listed as a “GLP-1 RA/amylin agonist,” was one of them. The same review found that almost half of the antiobesity drugs in phase 2 were incretin analogs. Weird thing to say about any market. Half the queue is the same idea.</p>

There are, roughly, three ways to read the amylin comeback</h2>
The first reading is the biology one. GLP-1 drugs reduce appetite, amylin drugs reduce appetite through a different route, and two routes beat one. CagriSema is described by the American Diabetes Association as “a fixed-dose combination of semaglutide (a GLP-1 receptor agonist) and cagrilintide (an amylin analogue).” That is about as simple as drug design gets: take a good drug, add a second good drug, sell them together. Amylin turns out to be a very sexy partner here. It hooks up with semaglutide in one product, and both sides seem to get more out of the arrangement than either did alone. That’s fine. Plenty of good medicine is just two things in one box.</p>
For scale, tirzepatide, a dual GIP/GLP-1 agonist, produced 19.5% and 20.9% mean weight reduction at its 10mg and 15mg doses in the SURMOUNT-1 trial. CagriSema’s 22.7% is a bigger number. But those were different trials with different people, and comparing headline numbers across trials is a thing everyone does and everyone is told not to do. One reading is that amylin adds real weight loss on top of GLP-1. Another is that the gap between two separate trials is small enough that it mostly tells you both approaches are very good, and not much about how much the amylin half is pulling. The sources here do not pick between those.</p>
The second reading is the business one. If half of phase 2 is incretin analogs, then having a GLP-1 drug is not a differentiator. It is table stakes (the phrase every strategy deck reaches for, and now this article too). It is like a basketball league where every team signed the same point guard, and now the whole game is who has the best forward. Somewhere in a pharma strategy meeting, someone said, “Okay, everyone has a GLP-1. What’s our GLP-1-plus?” and someone else said, “There’s this satiety hormone nobody is using.” I feel like this reading is true and also not a criticism. Companies need a reason for their drug to exist, and a second mechanism is a pretty good reason.</p>
The third reading is the least comfortable. Maybe adding amylin is not just about going higher but about the fact that one hormone runs out of road. The amycretin review’s phrase is “overcome metabolic plateaus,” which assumes plateaus are a problem worth engineering around. And a separate review, titled Restoring Satiety After GLP-1/GIP Pharmacotherapy, notes that weight regain after stopping GLP-1/GIP therapy “is associated with alterations in the hunger-satiety axis, including increased ghrelin and reduced leptin signalling.” The same review says plainly: “It remains unclear whether pharmacological suppression of appetite by GLP-1/GIP agents results in sustained normalisation of endogenous satiety regulation after treatment cessation.” Translated: nobody knows yet whether these drugs fix the body’s own fullness system or just override it while you take them. If it is override, then stacking amylin on top is not a cure for the plateau. It is a second override. Which might be fine, or might mean the long-run business is selling more switches forever.</p>

How you put amylin and GLP-1 in one molecule</h2>
The combination approach is two drugs. The more ambitious approach is one molecule that does both jobs, which is what amycretin is.</p>
How does one peptide talk to several receptors? Structural work on incretin receptors describes a two-step binding model for the receptor family called class B1, which are “polypeptide hormone receptors characterized by having a large N-terminal extracellular domain.” Residues near the tail end of the hormone (the C-terminus) grab onto that big outer domain. Residues near the front end (the N-terminus) reach into the part of the receptor that crosses the cell membrane and actually transmit the signal. So a peptide is sort of a key with a handle and a blade, and designers can tinker with each end. Whether that exact model transfers neatly to amylin and calcitonin receptors is not something these sources settle, so take it as the general shape of the problem, not a blueprint.</p>
Amycretin’s results so far come in two forms. As an oral drug, it showed 13.1% weight loss at 12 weeks. As an injection, 24.3% over 36 weeks. Those are different durations and different routes, so the two numbers are not a contest. They are a sign that the same molecule is being pushed down both paths at once.</p>

What the next amylin drugs look like</h2>
The next step is the one GLP-1 already took: get rid of the peptide entirely and make a pill out of a small molecule. Lilly’s orforglipron did this for GLP-1 (its FDA decision date moved from March 28 to April 10, 2026, which is the most pipeline-ish sentence I will write today). Structure Therapeutics is trying the same thing for amylin with ACCG-2671, described as “a novel oral small-molecule DACRA with high binding affinity at human calcitonin receptor (CTR) and amylin receptor (AMY3R).” DACRA means dual amylin and calcitonin receptor agonist. In obese rats it showed dose-dependent weight loss, “with additive effects in combination with semaglutide.”</p>
Between us, “additive effects in rats” is a sentence that has preceded a lot of drugs and a lot of non-drugs, and rats are not people. Anyway, it is early. But the shape of the bet is clear: an amylin pill to sit next to a GLP-1 pill, or whatever combination survives the trials.</p>
None of this is settled. CagriSema and amycretin have strong numbers, the small-molecule amylin work is preclinical, and the basic question of whether appetite drugs reset anything is open. It is a little dumb that the second-most-important satiety hormone in this pipeline spent years as a footnote, lol, but drug development runs on what is fundable, and for a while one hormone was enough.</p>
Hunger, it turns out, has more than one switch, and the plan is to press them all.</p>

CagriSema: Pairing Semaglutide With Amylin

2026-11-01T00:00:00+00:00

Novo Nordisk ran a trial in which 2,108 people got its new drug and 302 people got its old drug. The new drug was the old drug plus another drug. (This is a perfectly normal thing to do in drug development, and also a slightly funny thing to do, and we will get to both.)</p>

CagriSema is Novo Nordisk’s combination of semaglutide, the molecule it already sells as Ozempic for type 2 diabetes and Wegovy for weight loss, with cagrilintide, an amylin analogue. In REDEFINE 1, its main obesity trial, people on the combination lost an average of 22.7% of their body weight at 68 weeks under one way of counting and 20.4% under another, against 2.3% to 3.0% on placebo. Semaglutide alone got 14.9%. By any ordinary standard that is a very large result. The market’s reaction was more muted than that, and the reason has less to do with the drug than with the yardstick.</p>

Why you would bolt a second drug onto your best seller</h2>
Start with who gets paid for what. Novo gets paid for semaglutide. Semaglutide has also piled up evidence beyond weight. The SOUL trial showed fewer major cardiovascular events with the oral version. The FLOW trial supports kidney and heart protection in people with type 2 diabetes and kidney disease. It also improves symptoms in obesity-related heart failure with preserved ejection fraction. That is a lot of work already done on one molecule.</p>
Then a different molecule, tirzepatide, which Novo does not sell, showed up. SURMOUNT-5 was a head-to-head trial of tirzepatide against semaglutide for obesity, and in the Japanese obesity-disease subgroup at week 72, tirzepatide beat semaglutide by 7.2 percentage points of body weight. (The site’s tirzepatide article covers how it manages that.) So Novo needs a next product.</p>
Here is the appeal of a combination. You keep the molecule you know how to make, the one with outcomes data, and you add a second one that works through a different hormone system. The NEJM paper describes it plainly: “CagriSema is a fixed-dose combination of semaglutide (a GLP-1 receptor agonist) and cagrilintide (an amylin analogue).” Presumably the hope is that the two add up. (The amylin article on this site explains why anyone thinks they would.)</p>

How REDEFINE 1 was built, and who got what</h2>
If you sell a combination, you have to show that each half earns its place, which means a trial with arms for the combination, each piece alone, and placebo. REDEFINE 1 randomized 3,417 people in a 21:3:3:7 ratio: 2,108 to CagriSema, 302 to semaglutide, 302 to cagrilintide and 705 to placebo.</p>
The lopsided ratio makes sense. You want lots of safety data on the thing you plan to sell. You need only enough people in the single-drug arms to show the combination beats them. I suppose the semaglutide arm is a little strange from Novo’s side, since the comparator is its own blockbuster, and the goal is to make it look worse.</p>
It did. A post hoc analysis looked at how many people got both their BMI under 27 and their waist-to-height ratio under 0.53 by week 68: 30.3% on CagriSema, 19.1% on semaglutide, 9.0% on cagrilintide, 3.3% on placebo. Each piece helps. Together they help more.</p>

Which number is the number</h2>
Trials like this report results under different estimands, which are ways of handling people who stop taking the drug. The treatment-policy estimand counts everyone as randomized, quitters included, and gave CagriSema 20.4% against 3.0% for placebo. The adherence estimand asks what happens to people who actually stay on it, and gave 22.7% against 2.3%.</p>
Both are legitimate. They answer different questions. The press-release headline used 22.7%. I’m sure that choice was made after long and genuine reflection on which question the public most wanted answered.</p>
The second obesity trial, REDEFINE 2, in people with type 2 diabetes, came in lower: 13.7% against 3.4% placebo on treatment policy, 15.7% against 3.1% on adherence. People with diabetes tend to lose less on these drugs, so this is not a scandal. It is just a smaller number.</p>

Why the CagriSema market reaction was what it was</h2>
The sources here do not record the share price move, or what number investors had penciled in beforehand, so I won’t state either. What is settled is how the comparison works, and the comparison is not against placebo. It is against tirzepatide.</p>
Here is the call you can picture, invented but not hard to invent. “Congratulations on the result,” an analyst says. “Can you walk us through the gap to tirzepatide?” Nobody on that call is asking about placebo.</p>
A 2026 network meta-analysis, which stitches separate trials together against a common placebo, put tirzepatide 15 mg at 17.97% weight reduction versus placebo and CagriSema at 17.84%. The difference is 0.13 percentage points. Thirteen hundredths. For a 200-lb person, that is about four ounces of body weight, roughly a sandwich, across more than a year of treatment. It is well inside the noise of comparing trials that were never run against each other. It is also, for marketing purposes, second place.</p>
And second place with two molecules instead of one. Making two peptides costs more than making one, presumably. A 2026 meta-analysis found injection-site reactions about three times as frequent as with semaglutide alone (RR 3.14), though gastrointestinal side effects were not significantly increased. So the pitch becomes: as good as the rival, more complicated to make. It’s fine. It is just not the pitch anyone wanted.</p>
It is like running a marathon in a personal best and learning that the guy who started next to you finished at the same moment, carrying less.</p>

What REIMAGINE 2 and the meta-analyses added</h2>
REIMAGINE 2 tested CagriSema in type 2 diabetes against semaglutide at two doses each, plus cagrilintide and placebo. At the top doses, weight loss at 68 weeks was 14.2% versus 10.2% (efficacy estimand) or 12.9% versus 9.2% (treatment regimen). HbA1c fell 1.91 points versus 1.76 from a baseline of 8.2%. Novo Nordisk’s announcement said CagriSema showed “superiority over semaglutide on both weight loss and HbA1c across all tested doses.” Novo said it would approach regulators about a type 2 diabetes pathway after REIMAGINE 1 and REDEFINE 3.</p>
The 2026 Frontiers meta-analysis, covering 5 trials and 4,746 people, agreed on weight: 6.89 percentage points more loss than semaglutide 2.4 mg, about twice the chance of losing 20% or more. On blood sugar across all populations, it found “no incremental glycemic benefit.” Is that a contradiction? Not really, I guess. A 0.15-point edge in a diabetes trial can be statistically superior and still vanish when you pool in people without diabetes, who have less blood sugar to lower.</p>

Where the chain ends</h2>
Look, the logic of adding a molecule doesn’t obviously stop at two. (A made-up example, and only that.) Version three adds a third hormone and the ratio becomes 21:3:3:3:7. Version five needs a single-agent arm for every component, so most of the trial budget is spent proving each ingredient is individually worse than the whole. By version nine the only arm everyone fully understands is placebo, and the press release is mostly a table of estimands. Structure Therapeutics is already working on an oral small molecule hitting amylin and calcitonin receptors that showed additive effects with semaglutide in obese rats, so the stacking instinct is not unique to Novo.</p>
I don’t know how CagriSema will be priced or positioned, and nothing here settles it. What the chain does show is where the incentives landed. Novo built a trial where most people got the new drug and a few got the old one, to prove the new one was better. It was better. Then the market ran its own trial in its head, with tirzepatide in the small arm, and scored it in hundredths.</p>
A fifth of body weight is the baseline now.</p>

The GIP Receptor: Agonist or Antagonist?

2026-11-01T00:00:00+00:00

I spent part of this week reading one sentence from a scientific review the way you would read an indemnification clause, slowly and with suspicion, and I have come to think it is the best sentence in obesity drug development. It is about the GIP receptor, the receptor for glucose-dependent insulinotropic polypeptide, which is one of the two gut hormones called incretins. Like its better-known sibling, the GLP-1 receptor, it sits on the insulin-making cells of the pancreas, and a structural biology paper on incretin receptors says plainly that “incretin receptor agonists stimulate the synthesis and secretion of insulin from pancreatic β-cells.” (It shows up elsewhere too. Rat pancreatic alpha cells, for instance, turn out to carry working receptors for both hormones.)</p>

So should a drug turn that receptor on or turn it off? The industry’s answer is yes (which is also what a toddler says when you offer a choice between two desserts). Tirzepatide is a dual agonist: it switches on the GIP receptor and the GLP-1 receptor. Maridebart cafraglutide, also called MariTide or AMG 133, is a bispecific antibody that switches on the GLP-1 receptor and blocks the GIP receptor. Both are pitched as doing better than switching on GLP-1 alone, and the honest summary of why is that nobody has settled it.</p>

The sentence, and what the GIP receptor fight is about</h2>
Here is the sentence, from a review titled “The Premise of the Paradox: Examining the Evidence That Motivated GIPR Agonist and Antagonist Drug Development Programs”:</p>
“The paradox that both GIPR agonism (tirzepatide) and GIPR antagonism (maridebart cafraglutide) provide additive weight loss when combined with a GLP-1 receptor agonist is a central unresolved scientific question in incretin pharmacology.”</p>
I mean, that is a whole field in one sentence. Let’s take it clause by clause, as if somebody might sue over it.</p>

“Both GIPR agonism and GIPR antagonism”: who is on each side</h2>
An agonist activates a receptor. An antagonist blocks it. In ordinary pharmacology these are opposites, the way the gas pedal and the brake are opposites, and you would expect them to have opposite effects on whatever the receptor controls.</p>
The sentence names one champion for each side. In the agonist corner is tirzepatide, “a 39-amino-acid synthetic peptide” (per a cardiology review) that mimics both hormones at once. In the antagonist corner is maridebart cafraglutide, which is not a peptide at all but an antibody built to grab two different receptors and do opposite things to them. (Agonist on one, antagonist on the other, in a single molecule, which is the kind of flexibility you normally only see in consultants.)</p>
It is worth noticing that both sides actually built drugs. Nobody spends years and a great deal of money developing a molecule on a hunch. The review’s own title tells you there was “evidence” that “motivated” both programs. Each team looked at what was known about GIP and concluded, sensibly from where it stood, that its direction was the right one. The team pushing activation had a hormone whose whole job description is releasing insulin; the team pushing blockade presumably had its own reasons to think less GIP signaling would mean less fat. Both were reading real data.</p>
They just disagreed about the sign.</p>

What “additive” is doing in the GIP receptor paradox</h2>
“Additive” is a precise word. It does not say that GIP agonism causes weight loss on its own, or that GIP blockade does. It says that each adds something on top of a GLP-1 drug.</p>
The numbers that make the agonist side look additive are fairly clean. One pharmacodynamics review puts GLP-1 receptor agonists at “approximately 6-15% weight loss in clinical trials” and dual GIP/GLP-1 agonists such as tirzepatide at approximately 15-20%. In the SURMOUNT-1 phase 3 trial, tirzepatide produced mean weight reductions of 19.5% at 10mg and 20.9% at 15mg. For the antagonist side, the facts in front of me describe maridebart cafraglutide as “in clinical development” and do not give a weight-loss figure, so I won’t make one up.</p>
But look at how “additive” gets measured. It works like splitting a dinner bill by subtraction: you know roughly what the table would have spent without your friend, you see the final check, and whatever the difference is gets assigned to the friend (who, for all the math knows, only had water). That tells you the total changed when he showed up. It does not tell you what he ordered. A GIP component that pushes the receptor and a GIP component that blocks it can both leave the check bigger, and the subtraction method will cheerfully credit each of them.</p>

“When combined with a GLP-1 receptor agonist” is the load-bearing clause</h2>
This is the clause that keeps the paradox from being simply a contradiction. Neither drug is a pure GIP drug. Both arrive attached to a GLP-1 agonist, and GLP-1 agonists already “reduce appetite, delay gastric emptying, and enhance glucose-dependent insulin secretion,” to borrow a pediatric obesity review’s list. Whatever GIP is doing, it is doing it in a room where GLP-1 is already doing most of the talking.</p>
And the two GLP-1 halves are not the same thing. One is part of a 39-amino-acid peptide. The other is part of an antibody. They differ in size, in how long they last, in where in the body they can reach. So when you compare “GLP-1 plus GIP-on” against “GLP-1 plus GIP-off,” you are not really holding the GLP-1 constant. It’s fine as a description of two products. It is less fine as a controlled experiment.</p>
I picture a lab meeting somewhere: “Okay, so it works when we turn it on, and it works when we turn it off.” “Great. Does it work when we leave it alone?” “That’s the GLP-1 arm.”</p>
It is a bit like the Seinfeld episode where George Costanza decides to do the opposite of every instinct and his life improves, except here both the instinct and the opposite improved things, which is not how that episode went.</p>

“Unresolved” means unresolved</h2>
The last clause is the most honest one. “A central unresolved scientific question” is a review telling you, in its own words, that the field does not know. I don’t know either, and the facts I have do not rank the competing explanations, so I’ll describe the shapes an answer could take rather than pretend one has won.</p>
One shape: the two drugs are not really doing opposite things over time. A receptor that is pushed hard for weeks might respond differently than one nudged for a minute, and the line between “activating it a lot” and “blocking it” might be blurrier than the textbook vocabulary suggests (the relationship between these drugs and this receptor is, let’s say, complicated). Another shape: the GIP receptor does different jobs in different tissues, so turning it on in one place and off in another could both point toward weight loss. A third shape: GIP is sort of a passenger, and the gap comes mostly from the different GLP-1 machinery in each molecule.</p>
There are also mechanism papers that complicate things in their own way. One proposes that dual and triple agonists of the GLP-1, GIP and glucagon receptors “promote thermogenic-like amino acid profiles” in brown fat, with “robust heat production.” That is a story about agonists burning energy. Even if it holds, it does not obviously explain why an antagonist would help too.</p>
None of this has stopped anyone from building more drugs. Multi-agonists keep arriving; UBT251, a triple agonist of the GLP-1, GIP and glucagon receptors, showed weight loss of -13.6% to -19.7% versus -2.0% on placebo in a 205-person, 24-week phase 2 trial. Those programs all turn the GIP receptor on. The antibody turns it off. I guess the market will run the experiment the biology hasn’t finished.</p>
Meanwhile the agonist side already has its branding sorted out. Tirzepatide’s “unique dual mechanism,” according to that cardiology review, earned it “the nickname ‘twincretin.’”</p>

The GLP-1 Pipeline: Every Serious Contender in One Place

2026-11-01T00:00:00+00:00

A 2024 systematic review of emerging obesity drugs counted 14 ongoing phase 3 trials, and the list reads less like a drug class than like a group chat. There’s retatrutide, which hits three receptors. There’s CagriSema, which is two drugs sharing one product. There’s orforglipron, which is a pill. There are mazdutide and survodutide, which hit GLP-1 and glucagon, and ecnoglutide and TG103, which are plain GLP-1 receptor agonists, and also, sitting in the same list, dapagliflozin and a sibutramine/topiramate combination.</p>

So here is the glp-1 pipeline in one sentence: it sorts along two questions, which receptors the molecule touches and how it gets into the body. On receptors, the options are GLP-1 alone, GLP-1 plus GIP (tirzepatide is the established example), GLP-1 plus glucagon, all three at once, GLP-1 plus amylin, and one oddball that activates GLP-1 while blocking GIP. On delivery, it’s mostly injected peptides plus a growing set of oral small molecules, led by orforglipron. Which of these wins is not settled, and a good chunk of the field is still in phase 2.</p>

Why build another version of a drug that already works?</h2>
The sensible reaction to all this is: the drugs work already, so why are there so many of them? Tirzepatide produced mean weight reductions of 19.5% and 20.9% at its 10mg and 15mg doses in the SURMOUNT-1 phase 3 trial. GLP-1 receptor agonists reduce major cardiovascular events, and the SELECT trial extended that benefit to people with cardiovascular disease and obesity but no diabetes. At some point a product category is just done, and everybody else is making toothpaste.</p>
That objection is reasonable, and the answer is weirder than “competition.” The pipeline is not a dozen copies of one drug. It is a dozen different arguments about what the drug should be in the first place. Some of those arguments contradict each other. Some of the contradictions are both producing weight loss in trials. That’s the fun part.</p>
(I should admit that “reading receptor pharmacology papers on a Sunday” is how I relax, which says more about me than about the papers.)</p>

The multi-agonists: one peptide, several doorbells</h2>
The original idea is simple. GLP-1 is a gut hormone, its receptor sits on cells in the pancreas and brain and elsewhere, and a drug that activates that receptor lowers blood sugar and appetite. Then someone noticed you could build a single peptide that rings more than one receptor. Tirzepatide is a 39-amino-acid synthetic peptide that activates both the GIP and GLP-1 receptors, a design that, according to one cardiology review, earned it the nickname “twincretin.” In phase 3 it beat GLP-1 monotherapy on blood sugar in the SURPASS trials and on weight in the SURMOUNT trials.</p>
Once two works, three is obvious. Retatrutide is a triple GLP-1/GIP/glucagon agonist. UBT251 is another one, and in a phase 2 trial of 205 adults with obesity over 24 weeks it produced weight loss of 13.6% to 19.7%, versus 2.0% on placebo. A 2026 review said GLP-1/glucagon duals and triples like retatrutide “have exhibited unprecedented weight-loss efficacy,” which is the sort of sentence review authors get to write about once a decade.</p>
Why glucagon, a hormone that raises blood sugar? The pitch is that GLP-1/glucagon agonism raises energy expenditure by stimulating fat oxidation, which is a different lever from the appetite-focused GLP-1/GIP approach. Mazdutide and survodutide are the duals built on that idea. The structural biology here is fiddly: cryo-EM work on dual GLP-1/glucagon peptides (including cotadutide and SAR425899) found that the first three residues of the peptide engage the two receptors differently, and the middle of the peptide reshapes a loop of the GLP-1 receptor on binding. Selectivity comes down to a few side chains pointing slightly different ways.</p>
I’m contractually required to imagine the endpoint. Here is a made-up scenario. A medicinal chemist walks into a Monday meeting and says, “Hey guys, what if we also hit glucagon.” Everyone nods. The next Monday it’s amylin. Then calcitonin. Then, why not, the receptor for some hormone that governs how much you enjoy jazz. By year five the team has a molecule that activates every receptor in the human body, which is technically a full agonist of being alive, and the phase 1 readout is just the word “yes.” This is dumb, obviously. But the direction of travel is real.</p>

Amylin, and the question of one molecule or two</h2>
The amylin branch makes the structural choice explicit. CagriSema is a fixed-dose combination of semaglutide and cagrilintide, an amylin analogue: two molecules sharing one product, a perfectly ordinary arrangement between consenting peptides. Amycretin goes the other way and puts GLP-1 and amylin agonism into a single molecule (one source counts calcitonin receptors as a third target). It reached 13.1% weight loss at 12 weeks given orally and 24.3% over 36 weeks given by injection.</p>
The cleanest comparison is a restaurant bill. CagriSema is two diners asking for separate checks: each drug keeps its own pharmacology, its own dose, its own half-life. Amycretin is one check with two items on it, which is tidier to carry but means you can’t adjust one item without reprinting the whole receipt. Neither is obviously better. Which one patients and regulators end up preferring is not settled by the facts here.</p>

The GIP paradox in the GLP-1 pipeline</h2>
Now the strange part. Tirzepatide activates the GIP receptor and adds weight loss on top of GLP-1. Maridebart cafraglutide (Amgen’s MariTide, AMG 133) is a bispecific antibody that activates the GLP-1 receptor while blocking the GIP receptor, and it is also in development because blocking GIP also seems to add weight loss. A review titled “The Premise of the Paradox” calls this “a central unresolved scientific question in incretin pharmacology,” which is the polite academic way of saying the arrows point in opposite directions and both hit the target.</p>
One reading is that GIP biology is two-sided and both handles turn the same valve, for reasons nobody has fully written down. A second reading is that the GIP part matters less than the branding suggests, and most of the work in both drugs is being done by the GLP-1 half, with GIP along for the ride in whichever direction. The data cited here do not choose between them. I feel like that should bother people more than it does, but anyway, both programs exist and are spending money.</p>

Pills, which are a different business entirely</h2>
The oral branch is less about biology than about manufacturing and convenience. Peptides are big and fragile and the stomach chews them up, so the alternative is a small, non-peptide molecule that fits into the receptor without being a hormone at all. Orforglipron, from Eli Lilly, is one. Lilly described it in a press release as “the first oral small-molecule GLP-1 receptor agonist to successfully complete a Phase 3 trial,” where it lowered HbA1c by 1.3% to 1.6% across doses, and the company positions it as potentially the first oral GLP-1 agonist approved specifically for obesity. Behind it are HRS-7535, which showed efficacy in a phase 2 diabetes trial in people already on metformin and SGLT2 inhibitors, and aleniglipron, with phase data published in Nature Medicine in 2026.</p>
You and I both understand that the receptor does not care whether it was reached by a pill or a pen. The pill matters because of everything around the receptor: supply, cost, people who would prefer not to inject, or whatever else drives a prescribing decision. That’s fine. It is still a real scientific achievement to get a non-hormone to do a hormone’s job.</p>

Bias, the drug that only delivers half the message</h2>
The last axis is the most abstract. The GLP-1 receptor signals mainly through a G protein called Gs, but it also recruits a protein called beta-arrestin, and a drug can be built to favor one route. A study of one nonpeptide agonist, LY3502970 (also called OWL833), found it binds a unique pocket in the upper part of the receptor and acts as a partial agonist biased toward G protein over beta-arrestin. Other work found that the outward displacement of one extracellular loop, ECL3, is what distinguishes G protein-biased states, and that small changes to the front end of GLP-1 itself can produce bias. One 2026-era review lists multi-agonists, biased agonists and oral formulations as the three main axes of next-generation development.</p>
The point is that the pipeline isn’t one race. It’s three or four races run on the same track, and some runners are entered in several. Safety, so far, looks similar across the class in pooled data: a 2026 systematic review found serious adverse events in 6.5% of GLP-1 drug recipients versus 5.2% on placebo. Fine, not nothing.</p>
And since activating GIP helps and blocking GIP also helps, the obvious next entrant is a molecule that does nothing at all at the GIP receptor, which would be the third GIP strategy, the cheapest to make, and, lol, already on the market.</p>

'GLP-3' Is Not a Hormone: What People Mean When They Say It

2026-11-01T00:00:00+00:00

I spent part of this week reading about a hormone that does not exist, which in this corner of drug development is more normal than it sounds. If you typed GLP-3 into a search engine, here is the short answer: there is no such hormone, no such receptor, and no recognized class of drugs by that name. It is a nickname.</p>

The nickname mostly points at retatrutide, an experimental weekly injection that a review on hormone-receptor drugs for chronic kidney disease describes, accurately and without excitement, as “a triple GLP-1/GIP/glucagon receptor agonist.” It hits three receptors. GLP-1 is famous, so a drug that works on three pathways gets called the three version (the arithmetic is doing a lot of work here). That arithmetic is wrong, but it is wrong in an instructive way, and following it shows who gets paid for what in the business of naming molecules.</p>

What the “1” in GLP-1 actually counts</h2>
GLP-1 is glucagon-like peptide-1, a hormone made in the gut. A structural paper that imaged the activated GLP-1 receptor with cryo-EM summarizes its job as having “essential roles in regulating insulin secretion, carbohydrate metabolism, and appetite.” The “1” is part of the hormone’s name. It is not a tally of receptors, pathways or anything a drug does, and a drug does not move up the numbers by doing more.</p>
The receptors involved are cousins. Pharmacologists call them class B1 GPCRs, which are polypeptide hormone receptors with a large outer section called the N-terminal extracellular domain. Binding is described by the “two-step binding model,” in which residues near the hormone’s tail end first “interact with the N-terminal ECD of the receptor,” and only then does the front end move inward to “transmit signals.” So the hormone gets acquainted at the door before it is invited in. Very proper.</p>
The family resemblance is, I guess, what makes it plausible to ask one peptide to stand in for several hormones at once. That is the design bet behind tirzepatide (two receptors) and retatrutide (three). None of it creates a new hormone. It creates a molecule that some receptors mistake for their own.</p>

How three receptors turned into GLP-3</h2>
Here is the chain, one link at a time.</p>
The first link is the drug companies, which get paid for molecules that beat the last molecule. A review of GLP-1 receptor biology lists dual and triple agonists as one of “the three major axes of next-generation incretin drug development,” alongside biased signaling and pills. Adding receptors is a product strategy, and the trial numbers have rewarded it so far. Tirzepatide, the dual GIP/GLP-1 agonist, produced mean weight reductions of 19.5% and 20.9% at its 10 mg and 15 mg doses in the SURMOUNT-1 phase 3 trial. Retatrutide, in the phase 3 TRIUMPH-1 trial, produced mean weight loss of 28.3% at 80 weeks on the 12 mg dose, 25.9% on 9 mg and 19.0% on 4 mg. AJMC reported the 12 mg figure as “a mean weight loss of 70.3 lb (28.3%) at 80 weeks, from a baseline average body weight of 248.5 lb.” (How the trial counted people who stopped treatment matters a lot here, and the site’s careful read of those results handles it.)</p>
The second link is the official names, which are not built for talking about at dinner. “Retatrutide” is a word most people mistype at least once (I have managed it several times in this article alone). So writers reach for nicknames, and the field has precedent: a cardiology review of tirzepatide notes that its “unique dual mechanism” earned it “the nickname ‘twincretin.’” That one at least used a real category, the incretins, and added a real count.</p>
The third link is the public, which already knows one term. GLP-1 became shorthand for a whole drug category, the way a brand name becomes a verb. Once that happens, a drug that does more than GLP-1 needs a bigger number, the way a sequel needs one (nobody went to see Toy Story 3 thinking it was about three toys). Naming a drug by its receptor count this way is like a landlord numbering apartments by how many bedrooms they have: the label tells you something true about the unit, and it will reliably send the mail carrier to the wrong door.</p>
The fourth link is search engines and the websites that live off them. People type what they have heard, so pages appear that answer what people typed. Somewhere an editor says, “Can we get a GLP-3 explainer up by Friday, the traffic is just sitting there.” This article is, in some sense, that explainer. Lol.</p>
And here is where the chain arrives: a drug class that does not exist now has explainers, comparison pages and search volume, which is most of what a drug class has in public life. Nobody planned this. Each link did the locally sensible thing.</p>

Why glucagon makes the nickname stranger</h2>
The third receptor retatrutide hits is the glucagon receptor. GLP-1 means glucagon-like peptide. So the nickname takes a drug that activates actual glucagon receptors and names it after a hormone defined by resembling glucagon, then adds a number as though the imitation had a sequel. It is a strange compliment.</p>
The glucagon piece is also not decorative. A review of glucagon signaling notes that mazdutide, survodutide and retatrutide all “incorporate GLP-1 receptor-activating moieties to counteract glucagon’s hyperglycaemic effects.” Glucagon raises blood sugar, which is an awkward property for a metabolic drug, so the GLP-1 component partly exists to cancel it out. Another review argues that GLP-1/glucagon agonism adds energy expenditure, by stimulating fat oxidation and glucose production, rather than relying mainly on appetite. Why a weight-loss drug would want glucagon at all is its own long story, told elsewhere on this site.</p>
So the receptor that does the most distinctive work in the molecule is the one the nickname leaves out. Typical, really.</p>

Does GLP-3 even mean one drug?</h2>
Not really. Retatrutide is not the only triple. UBT251, a triple GLP-1/GIP/glucagon agonist linked to Novo Nordisk, produced weight loss of 13.6% to 19.7% versus 2.0% for placebo in a phase 2 trial of 205 adults in China over 24 weeks. By the nickname’s arithmetic, that is also GLP-3. A label that fits every three-receptor molecule is a category, and the explainer comparing retatrutide with semaglutide and tirzepatide says flatly that the label “does not correspond to any recognized scientific drug class.” So it is a category that the people who define categories say is not a category. Fine for search, I suppose, but dumb for anything else.</p>
Now a scenario, clearly made up. Suppose a company adds amylin, the satiety hormone already paired with GLP-1 in CagriSema and amycretin, to a triple agonist. The internet calls it GLP-4. A rival bolts on a fifth receptor and press releases start leading with the number. By the end of the decade there is a GLP-9 that activates receptors for appetite, insulin, liver fat, bone, sleep and possibly whether you finish a television series, and analysts are asking on earnings calls why the pipeline is “stuck at seven.” Pharmacologists keep writing “triple agonist” and “quadruple agonist” in their papers, which nobody searches for.</p>
The real version is less silly but has the same structure. Receptor count is easy to say and easy to compare. Whether a given receptor helps, and how much, is not easy to say. GIP is the cleanest example: tirzepatide activates the GIP receptor, while Amgen’s maridebart cafraglutide blocks it, and both seem to add weight loss to GLP-1 agonism. A paper examining that puzzle calls it “a central unresolved scientific question in incretin pharmacology.” A naming scheme that counts receptors cannot even tell agonism from antagonism.</p>

So what should people call it?</h2>
The accurate name is a triple GLP-1/GIP/glucagon receptor agonist, which no one will ever say out loud at a barbecue. Whether retatrutide reaches the market, and under what brand name, is not settled by the trial results so far; TRIUMPH-2, in adults with obesity and type 2 diabetes, reported smaller losses (18.8% at 12 mg versus 5.1% on placebo at week 80) and the regulatory path is still being walked.</p>
One reading is that GLP-3 is just an error, a misread number that stuck because it was convenient. The other reading is that it is, oddly, the most useful name the drug has, because it encodes the one fact the public actually wants (this is the next one, and it does more) in five characters. Those readings point in opposite directions and both seem true. For instance, a person who says GLP-3 at a pharmacy counter and a chemist who winces at it probably mean the exact same molecule.</p>
I spent the week reading about a hormone that does not exist, and by the end of it this article had become one more small reason that it sort of does.</p>

Why a Weight-Loss Drug Would Add Glucagon, of All Things

2026-11-01T00:00:00+00:00

Glucagon is the hormone your body uses to raise your blood sugar. When you have not eaten for a while, the pancreas releases it, the liver breaks down its stored glycogen, and glucose goes back into the blood. That is roughly the opposite of what a diabetes drug is for. Several of the most closely watched weight-loss drugs in development include glucagon activity anyway, on purpose, and it seems to help.</p>

A glucagon receptor agonist is a molecule that switches on the glucagon receptor (GCGR), which, in the words of a structural biology paper on this receptor family, “responds to glucagon by increasing blood glucose levels and promoting the breakdown of liver glycogen.” The receptor sits mostly in the liver and kidney, and to a lesser extent in other tissues. In obesity drugs it never shows up alone. It gets bolted onto GLP-1 activity, and sometimes GIP activity too, in molecules like mazdutide, survodutide and retatrutide. The short version of why: glucagon appears to make the body burn more energy and pull fat out of the liver, and the incretin parts of the molecule are there to clean up its blood-sugar mess.</p>

What the other drugs were doing before glucagon showed up</h2>
Most weight-loss drugs work on the eating side of the ledger. A 2026 review says traditional ones “primarily act by centrally suppressing appetite” through circuits in places like the hypothalamus. GLP-1 drugs reduce appetite, slow gastric emptying and boost insulin secretion when glucose is high. They get approximately 6 to 15% weight loss in trials. Add GIP, as tirzepatide does, and you get approximately 15 to 20%. In the SURMOUNT-1 phase 3 trial, tirzepatide produced mean weight reductions of 19.5% at 10 mg and 20.9% at 15 mg.</p>
That is a lot of eating less. At some point you run out of less.</p>
So the obvious next thing is the other side of the ledger: energy out. This is where glucagon comes in, and where I should admit that I write about this for a living and still sometimes have to stop and remember which direction glucagon pushes blood sugar. (Up. It pushes it up, which is the one direction a diabetes drug would prefer it did not go.)</p>

There are three ways to read the glucagon receptor agonist bet</h2>
There are, roughly, three ways to read this. The first is that glucagon makes you burn more. The second is that it is really a liver drug that happens to cause weight loss. The third is that the industry is deliberately buying a side effect and paying for its removal, and the price of removal is a lot of the result. They are not mutually exclusive. I feel like the third one gets less airtime than it deserves.</p>

Reading one: the drug turns up the furnace</h2>
Here is the cheerful version. One review of next-generation multi-agonists says dual GLP-1/glucagon agonism “increases energy expenditure by stimulating fat oxidation and glucose production,” which it describes as distinguishing it from the appetite-focused GLP-1/GIP approach. An industry article lists glucagon’s effects as stimulating energy expenditure, increasing fat oxidation and thermogenesis, triggering lipid breakdown and also reducing food intake. So it does a bit of the eating thing too. That’s fine.</p>
The mechanism stuff gets weirder the closer you look. One line of research proposes that dual and triple agonists trigger heat production in brown and beige fat by changing amino acid metabolism there. Another, in mice, found that glucagon receptor agonism regulates bile acid metabolism, and that adding bile acid binding resins (an old class of cholesterol drug) made glucagon-driven weight loss bigger. Its authors suggest bile acid signaling is “a key component” of how glucagon causes weight loss. In mice. Also, GLP-1 drugs alone may do some heat production of their own: liraglutide has been proposed to activate brown fat partly through thyroid hormone activation inside cells. So the furnace story is real but not tidy.</p>
There is a reason the furnace matters. A review on what happens after GLP-1/GIP treatment notes that weight loss often comes with a loss of fat-free mass, which “further lowers energy expenditure” and makes regaining weight easier after stopping. The body, having lost weight, quietly turns its own thermostat down. A drug that turns it back up is attacking that directly, at least in theory.</p>
Here is a made-up scenario to show the appeal. Imagine a household budget where the only lever is spending less on groceries. You cut groceries by a fifth. Then a fourth. Then the household starts eating the curtains. At some point a sensible financial adviser says “hey, have we considered earning more,” and everyone stares at him, because nobody had, and then they hire a second job that also, for some reason, sets the kitchen on fire a little. The fire is the blood sugar. We will get to the fire.</p>

Reading two: it is mostly a liver drug that also causes weight loss</h2>
The glucagon receptor lives mostly in the liver, so in some sense the liver is where you would expect the action. A review of glucagon signalling says that in early trials, mazdutide, survodutide and retatrutide each produced substantial weight loss while “improving liver health in those with MASLD.”</p>
The official name is metabolic dysfunction-associated steatotic liver disease (a name that, I assume, took a committee several meetings). Translated: the liver has too much fat in it, for reasons tied to the rest of your metabolism. Glucagon tells the liver to burn its fuel rather than store it, so a drug that does this is chewing on the problem from the inside. (The site has a separate piece on survodutide, which is the one most openly aimed at the liver.) There are also early data on cotadutide, a GLP-1/glucagon dual, suggesting benefits on albuminuria and cardiorenal risk markers, which fits a receptor that also lives in the kidney.</p>
On this reading, the weight loss is almost a pleasant side benefit of a molecule designed to drain a fatty liver. I suppose that would be a dumb way to describe something that produced double-digit weight loss, but drug development has done stranger things with its marketing.</p>

Reading three: buy a problem, pay to cancel it</h2>
The glucagon signalling review states the design rule flatly: mazdutide, survodutide and retatrutide all incorporate GLP-1 receptor-activating parts “to counteract glucagon’s hyperglycaemic effects.” Put plainly, the molecule contains one piece that raises blood sugar and another piece whose job is to lower it back down (a product spec that would get you laughed out of most engineering reviews outside pharmacology). The industry article says the GLP-1 and GIP activity in triple agonists “offsets” glucagon’s effect on blood sugar while keeping the energy-expenditure benefit.</p>
It is a bit like a basketball team signing a player who is incredibly fast and occasionally shoots at his own basket, and then signing two more players whose whole role is to block him. If it works, it works.</p>
And it does work, by the numbers. A network meta-analysis of 14 randomized trials of glucagon receptor agonists found retatrutide produced the largest weight reduction versus placebo: a mean difference of 13.44 kg. Look at that number for a second. Thirteen and forty-four hundredths of a kilogram, pooled across trials, with a 95% confidence interval running from 8.51 to 18.38. That is a range of almost ten kilograms, and the bottom of it is still more than eight kilograms. Statisticians call that a wide interval. Anyone else would call it a person’s worth of carry-on luggage, at minimum.</p>
Then look down the table. Survodutide: 10.74 kg. Mazdutide: 6.47 kg. Cotadutide: 3.41 kg, and not statistically significant, with a confidence interval that crosses zero. Retatrutide was also the only one whose blood sugar effect (HbA1c) reached statistical significance. Retatrutide, notably, is the one with the most incretin machinery attached, the one that adds GIP on top of GLP-1. Separately, an Annals of Internal Medicine review of 26 trials and 15,491 adults without diabetes found retatrutide at 12 mg weekly led with 24.2% weight loss, versus 17.8% for tirzepatide and 13.9% for subcutaneous semaglutide.</p>
Other triples are arriving too. UBT251, another GLP-1/GIP/glucagon peptide, produced 13.6% to 19.7% weight loss versus 2.0% on placebo over 24 weeks in a 205-person phase 2 trial (an article on it led with “up to 19.7%,” which is a perfectly normal way to write a headline, and also the most flattering one).</p>
That leaves the matter of which part is doing the work, and the uncomfortable reading is that the facts do not cleanly separate them. The glucagon parts that perform best are the ones most heavily wrapped in incretin activity, the meta-analysis found retatrutide and cotadutide less well tolerated than mazdutide, and the mechanism research is a pile of mouse bile acids and brown-fat amino acids. Nobody has settled what fraction of retatrutide’s result is glucagon burning fuel and what fraction is GLP-1 and GIP doing what they already did, plus mopping up after glucagon. Longer-term questions about lean mass, regain and safety, which reviews list as still open for the whole class, are not settled either. lol, it’s medicine.</p>
Glucagon is still the hormone that raises your blood sugar. It just turns out that, if you surround it with enough other hormones, it also makes you lose weight.</p>

Half-Life Engineering: How Incretin Drugs Went From Hours to Weeks

2026-11-01T00:00:00+00:00

Retatrutide, Lilly’s experimental drug that hits three hormone receptors at once, is injected once a week. That’s the useful fact. The gut hormones it imitates do nothing of the sort, and the distance between what your intestines release after lunch and what goes into a weekly pen is most of what this article is about.</p>

If you searched for the retatrutide half life hoping for a number of days, the sources this article relies on don’t give one. What they do settle is the schedule. In the phase 2 studies, doses ranged “from 0.5 mg to 12 mg weekly” in adults with type 2 diabetes and from 1 mg to 12 mg weekly in adults with obesity, and a systematic review of randomized trials describes the 12 mg dose as given once weekly. A drug injected weekly has to stay in the blood long enough to cover the week, so its half-life is long in the sense that matters. The exact figure isn’t settled here.</p>

What the retatrutide half life tells you, and what it doesn’t</h2>
A half-life is the time it takes for half of a drug to leave the blood. It’s a dull number that ends up deciding almost everything else (which is true of most numbers worth knowing). It sets how often people inject, how steady the drug levels are between doses, and in practice whether the product is something people will keep using for 80 weeks.</p>
And 80 weeks is the scale these trials run on now. TRIUMPH-1, the pivotal obesity trial, reported its topline on May 21, 2026, and AJMC wrote that retatrutide 12 mg “achieved a mean weight loss of 70.3 lb (28.3%) at 80 weeks.” (The results get their own careful article elsewhere on this site, so I’ll leave them there.) Results like that come from a molecule the body keeps around for days. Presumably nobody gets 28% off a drug that disappears before dinner.</p>

Why not just inject the hormone the body already makes</h2>
Here is the sensible objection. The body already makes GLP-1, GIP and glucagon. They already bind the right receptors. So why not bottle the real thing and skip the chemistry?</p>
It’s a fair question, because the natural hormones really are well designed for their receptors. A structural study of incretin receptors found that “ligands of incretin receptors adopt an α-helical conformation upon binding,” meaning the hormone coils into a spring shape and slots in. Evolution worked on that fit for a long time. It’s hard to improve.</p>
The trouble is that the body also designed these hormones to vanish. A post-meal hormone is a text message, not a billboard: it says “food arrived,” gets read, and gets deleted. Enzymes cut it up and the kidneys filter out the pieces. That’s correct behavior for a signal. It’s terrible behavior for a product.</p>
So the job is to make the hormone last longer. Actually, that’s not quite it, and the real version is stranger. The job is to build a molecule that still looks like the hormone to the one receptor that matters, and looks like nothing at all to every system the body uses to throw things away. The chemistry is less like making a sturdier hormone and more like teaching a hormone to sneak past security.</p>

Hiding from the enzyme: DPP-4 resistance</h2>
The first guard is an enzyme called DPP-4 (its name is the least interesting thing it does), which clips the front end off incretin hormones and leaves them inactive. Getting past it means changing the peptide at the spot the enzyme recognizes, using a substitute the enzyme can’t cut but the receptor will still accept.</p>
The constraint is tight. The structural study says the receptor’s outer domain “is important for ligand binding and ligand specificity,” while the part buried in the membrane handles activation. So every change risks breaking a handshake that took evolution a very long time to set up. You’re editing a key so one lock refuses it and a different lock still opens.</p>
(I’ve spent more of my working life than I’d like to admit reading about enzymes that chop up peptides, and I’m not sure I’ve won a single argument with one.)</p>
DPP-4 resistance alone doesn’t get you to a week, though. It gets you past the first guard. The kidneys are still there, filtering anything small, and a peptide is small.</p>

Hitching a ride on albumin: acylation</h2>
The second trick is acylation: attaching a fatty acid chain to the peptide. The fatty tail makes the drug cling to albumin, a large and abundant protein in the blood. Albumin is too big for the kidneys to filter, so while the drug is attached it is, in effect, invisible to the exit.</p>
You can picture the meeting where this started. “Hey, what if the drug just held onto something the kidney isn’t allowed to throw away?” (I made that up. I assume the real meeting had more slides.)</p>
It works sort of like valet parking. Your car is safe in the garage, and nobody can tow it, but you also can’t drive it until someone brings it back. A drug bound to albumin isn’t hitting receptors. It comes off a bit at a time, does its work, and the rest waits. A long half-life is really a slow, steady release from a protein the body won’t discard. And there is a nice symmetry in that: the same study that described the helix found that “hydrophobic interactions are the main driving force” for hormones binding their receptors. Greasiness gets the drug held in the blood, and greasiness gets it gripped at the receptor.</p>
The facts in front of me don’t say which of these tricks retatrutide itself uses, so I won’t guess.</p>

Bolting on something huge: Fc fusions and antibody conjugates</h2>
If hitching a ride on a big protein works, the next idea is obvious. Become the big protein.</p>
An Fc fusion attaches the active peptide to the Fc section of an antibody, the stem the body recognizes as one of its own durable proteins and recycles instead of destroying. An antibody conjugate goes further and links the peptide to an entire antibody. Either way the molecule is now huge, kidney filtration stops being a concern, and the body’s own antibody-recycling system keeps it in circulation. Amgen’s maridebart cafraglutide is the prominent antibody bet in this space, with its own article on this site, and it’s notable for blocking the GIP receptor rather than activating it, a paradox one review calls “a central unresolved scientific question in incretin pharmacology.”</p>
The tradeoffs are real and mostly not settled by anything I have here. A bigger molecule is a different molecule. It may reach tissues differently and need different manufacturing. Whether it’s better or worse than a small acylated peptide is a design argument, not a known result.</p>
Look, between us, the progression has a certain comedy to it. Step one, protect the hormone from an enzyme. Step two, attach a fat tail so it hides in a protein. Step three, staple it to an antibody, which is a little like protecting a letter from getting lost by mailing it inside a refrigerator.</p>

Why weekly is the number everyone aims for</h2>
The engineering is in service of a schedule, and the schedule is weekly. It’s purely a coincidence, I’m sure, that “once weekly” also fits neatly across the front of a box.</p>
It isn’t the only direction, mind you. A review of GLP-1 receptor biology lists the field’s three major axes as dual and triple agonists, “biased agonist design, and oral formulations.” The oral path abandons injected half-life engineering for small molecules like orforglipron, which produced weight loss of 11.2% at its 36 mg dose over 72 weeks in the ATTAIN-1 trial, and for peptides like amycretin, which a review reports at 13.1% loss over 12 weeks taken orally and 24.3% over 36 weeks injected. I don’t know which approach wins. Neither does anyone, which is what makes it a pipeline.</p>
What a long half-life buys, in principle, is steady exposure, with no peaks and troughs. That’s a reasonable lens for one detail Lilly reported from TRANSCEND-T2D-1: “No weight loss plateau was observed with retatrutide,” with participants still losing weight at 40 weeks. That steady exposure explains it is my inference, not the trial’s finding. I mean, plenty of other things could explain it too.</p>
(My job, for what it’s worth, is explaining to strangers why a peptide was given a fatty tail and an antibody chaperone. Nobody grows up planning on that.)</p>
It’s fine that the half-life number isn’t in the sources. The schedule tells the story anyway. The gut sends a brief text after lunch and deletes it within the hour. Retatrutide sends one a week, and an entire field went to considerable trouble to make sure nothing in the body can delete it.</p>

What Is an Incretin? The Gut Hormones Behind a Drug Revolution

2026-11-01T00:00:00+00:00

Your intestine sends your pancreas a memo before the sugar from lunch has finished arriving. The memo is a hormone, and the hormones that carry it are called incretins. The two that matter are GLP-1 (glucagon-like peptide 1) and GIP (glucose-dependent insulinotropic polypeptide). Their basic job is in one line of the paper “Structural basis for ligand recognition of incretin receptors”: agonists of these receptors “stimulate the synthesis and secretion of insulin from pancreatic β-cells.” The gut notices food, releases an incretin, and the pancreas makes and releases insulin.</p>

The “incretin effect” is the name for that extra insulin response, the part you get because the food came in through the gut and the gut said something about it. GLP-1 turned out to do more than talk to the pancreas. It also has roles in “carbohydrate metabolism, and appetite,” and both GLP-1 and GIP help the gut talk to the brain through several signaling pathways. That last part is why a diabetes hormone became the basis of the most crowded corner of obesity drug development. The headline promises thirty years from hormone to drug. The facts I am working from do not lay out that timeline step by step, so what follows explains why the delay makes sense rather than dating each step.</p>

What is an incretin actually paid to do?</h2>
It helps to think of the body as a series of employees who get paid for specific things. The gut gets “paid” (in the evolutionary sense, I mean, nobody is cutting checks) for reporting that food has arrived. The pancreas gets paid for getting blood sugar under control. An incretin is the message from the first employee to the second. It works a bit like a text that says “heads up, carbs incoming.”</p>
The receptors that pick up the message have a sort of two-part design. According to the same structural paper, the outer end of the receptor (the N-terminal extracellular domain, which is a fancy way of saying the part sticking out of the cell) handles grabbing the hormone and deciding which hormone counts. The part threaded through the membrane handles actually switching the receptor on. The hormones fold into a helix when they bind, and the main force holding them to the outer domain is hydrophobic interaction (the same basic reason oil droplets clump in water). The receptor has a mailbox and a doorbell. Different parts.</p>
The pancreas also has cells that make glucagon, the hormone that raises blood sugar, and incretins talk to those too. A study on rat pancreatic alpha-cells found that GLP-1 and GIP act on them “via a protein kinase A (PKA)-mediated mechanism to stimulate Ca2+-induced exocytosis.” Translated into one flat sentence: the incretins flip a particular internal switch in the glucagon cells, and that makes them release their contents. Meanwhile GIP, per one industry report, enhances the effects of GLP-1 and increases lipolysis, which is the breakdown of stored fat. So the incretin system is not one memo. It is a group chat.</p>

Why a good hormone is not yet a good drug</h2>
Here is the first link in the chain where the incentives stop lining up. The body wants a meal signal to be brief, as a general matter, because meals end and you don’t want the “food is here” alarm ringing all afternoon. A drug company wants nearly the opposite. It wants something that lasts, can be dosed rarely, and gets taken for a long time. Both are acting sensibly. The body is optimizing for lunch. The company is optimizing for a product that someone can actually use on a schedule (and, to be fair, for a product that keeps working, which is the point of medicine).</p>
So the work of turning an incretin into a drug is basically the work of taking a hormone designed to be fleeting and persuading it to stick around. I assume there was some meeting where a chemist said “okay, what if we keep the part the receptor likes and change everything the body uses to get rid of it,” and someone else said “sure, but it still has to fold into that helix.” (This meeting is invented, but some version of it presumably happened many times.) The site’s piece on half-life engineering covers how drugs went from hours to weeks; the short version is that it is hard. That is part of why it took decades.</p>
Durability on paper is not the same as durability in a person’s life, though. A 2026 narrative review comparing real-world and trial evidence found real-world discontinuation rates for incretin-based therapies of 20% to 50% within one year. Trials look better. In the TRIUMPH-2 trial of retatrutide, 965 of 1,152 participants (84%) completed the study drug through week 80. Trials have nurses, reminders and schedules. Real life has the rest.</p>

Once the incretin worked, everyone showed up</h2>
The next link: once GLP-1 drugs worked, the incentive for every drug developer became “do that, but more.” A 2024 systematic review, “Emerging pharmacotherapies for obesity,” searched trial registries and databases from 2012 to 2024 and found 53 phase 2 and phase 3 trials covering 36 emerging obesity drugs or combinations (4 of those trials were withdrawn or terminated). Almost half of the obesity drugs in phase 2 as of 2024 were incretin analogs. Completed phase 2 incretin trials showed mean weight loss from 7.4% to 24.2%. When a category works that well, the pipeline stops being a pipeline and becomes a queue.</p>
“More” mostly meant more receptors. Tirzepatide is a 39-amino-acid synthetic peptide that agonizes both the GIP and GLP-1 receptors, which earned it the nickname “twincretin” (pharmacology is not a field known for its restraint in naming). It is, in effect, a molecule built to hook up with two receptors at once, and in the SURMOUNT-1 phase 3 trial it produced mean weight reductions of 19.5% and 20.9% at the 10mg and 15mg doses. The site’s tirzepatide article handles the details.</p>
Then came three. Retatrutide hits GLP-1, GIP and glucagon receptors, and so does UBT251, which in a 24-week phase 2 trial of 205 adults produced weight loss of 13.6% to 19.7%, versus 2.0% on placebo. Adding glucagon is odd on its face, because glucagon raises blood sugar. The trick, per an industry report, is that the dual incretin activity offsets glucagon’s blood-sugar effect while keeping its boost to energy expenditure. You hire the guy who sets fires because he also heats the building, and you hire two firefighters to stand next to him. It is sort of the Ocean’s Eleven approach to receptor pharmacology: every specialist covers for someone else’s flaw.</p>

Where the incentive chain starts to get strange</h2>
Follow the money one more link and the science gets confusing. Tirzepatide activates the GIP receptor. Amgen’s maridebart cafraglutide, a bispecific antibody, blocks the GIP receptor while activating GLP-1. Both seem to add weight loss on top of GLP-1. A review titled “The Premise of the Paradox” calls this “a central unresolved scientific question in incretin pharmacology.” Pressing the button helps. Unpressing the button also helps. Nobody has settled why, and the site’s GIP receptor article lays out the competing explanations.</p>
The unresolved list is long, on the other hand, and not just at the receptor level. Reviewers flag gastrointestinal side effects, weight regain after stopping, loss of lean mass, and open long-term safety questions. Effects on gut microbiota “remain uncertain.” Long-term effects in adolescents on growth, puberty and bone are uncertain too. Meanwhile the internet has started calling retatrutide “GLP-3,” a label that does not correspond to any recognized drug class. There is no GLP-3. There is just marketing gravity.</p>
And the chain finally reaches Washington. BioSpace reported that the FDA delayed a decision on Lilly’s obesity pill orforglipron and other awardees of a voucher program, describing it this way: the Commissioner’s National Priority Voucher program “awards tickets to companies that pledge to comply with national priorities such as addressing a key unmet need, boosting domestic manufacturing, and aligning drug prices with President Donald Trump’s Most Favored Nation scheme.” Translated flatly: a faster regulatory review is available to companies that promise, among other things, to price drugs in line with a White House pricing plan. So the gut tells the pancreas about lunch, the pancreas tells chemists about a receptor, the chemists tell investors about a pipeline, the pipeline tells regulators about unmet need, and the regulators tell companies about pricing, manufacturing, etc.</p>
Nobody designed that sequence. Each step was a sensible response to the step before it. Nobody intended this one.</p>
The hormone orforglipron mimics evolved to arrive before the sugar does. By the same logic, a well-designed incretin drug now has to arrive before the pricing policy does, which makes lobbying the next frontier in half-life engineering.</p>

Maridebart Cafraglutide: Amgen's Antibody Bet

2026-11-01T00:00:00+00:00

Amgen is developing an obesity drug that blocks the GIP receptor, which is the same receptor Eli Lilly’s tirzepatide was built to switch on. Both approaches are supposed to help you lose weight when paired with a GLP-1 drug. Both do. The Amgen drug is called maridebart cafraglutide (also MariTide, also AMG 133), and a review titled “The Premise of the Paradox” describes it as “a bispecific antibody that combines GIP receptor antagonism with GLP-1 receptor agonism and is in clinical development as a novel obesity therapeutic.”</p>

So, plainly: it is an antibody with a GLP-1-type peptide attached. The antibody end blocks GIP signaling and the peptide end activates the GLP-1 receptor. It is not approved. Because it is built on an antibody, the expected selling point is a schedule less frequent than weekly. On the specifics people search for, though (the exact dosing interval, the phase 2 weight-loss percentages), the sources behind this article give no numbers, so I will not invent any. What I can explain is the design and why it is weird.</p>

What maridebart cafraglutide actually is</h2>
Most incretin drugs are peptides, short chains of amino acids modeled on gut hormones. Tirzepatide, for instance, is a 39-amino-acid synthetic peptide that activates both GIP and GLP-1 receptors, which got it the nickname “twincretin.” Retatrutide goes further and hits three receptors from one molecule, which took a lot of medicinal chemistry to manage. (The site has separate pieces on both, so I will leave them there.)</p>
Maridebart cafraglutide is a different kind of object. Its core is an antibody, a large protein the immune system normally uses to grab specific targets, aimed here at the GIP receptor to hold it shut. The GLP-1 activity comes from peptides joined to that antibody. Chemists call the result a conjugate. That is a formal word for two things bound together permanently, and here, as in some marriages, the main point of the arrangement seems to be that one partner gets to stick around longer.</p>

The dumb version: turn GIP up</h2>
Here is the simple story, the one you would tell at a dinner party (if your dinner parties are already going badly). GLP-1 is a gut hormone that lowers blood sugar and appetite. GIP is another gut hormone in the same family. If one hormone helps, two hormones should help more. So you build a molecule that activates both receptors.</p>
That is tirzepatide, and the results were good. In the SURMOUNT-1 phase 3 trial, adults with obesity lost an average of 19.5% of body weight at the 10 mg dose and 20.9% at 15 mg. Across the SURMOUNT and SURPASS programs, tirzepatide beat GLP-1-only drugs on weight and on blood sugar. The dumb version worked.</p>
That is about as clean as drug development gets. Pull the lever, get the result.</p>

The sophisticated version: turn GIP down</h2>
Now the long road. Suppose you look at the GIP receptor and conclude, for reasons involving fat tissue and energy storage, that GIP is better blocked than activated. Then you would want the opposite of tirzepatide: a molecule that blocks GIP while still activating GLP-1. Activating a receptor with a peptide is the usual approach. Blocking one is something antibodies are good at. So you take an antibody that blocks the GIP receptor and attach GLP-1 agonist peptides to it.</p>
This is the more sophisticated version. It requires a different modality, a different manufacturing process, and a theory of GIP that points the other way. And then it also produces additive weight loss when combined with GLP-1 agonism.</p>
The same review says it directly: “The paradox that both GIPR agonism (tirzepatide) and GIPR antagonism (maridebart cafraglutide) provide additive weight loss when combined with a GLP-1 receptor agonist is a central unresolved scientific question in incretin pharmacology.”</p>
Two companies pushed a receptor in opposite directions. They ended up in roughly the same place. It is a bit like two teams in the Super Bowl running toward opposite end zones and both being credited with the same touchdown.</p>

Why the paradox may not really be one</h2>
I should be careful here. I said both companies pushed the receptor in opposite directions. More precisely, they designed molecules that push in opposite directions in a test tube, and what happens to the receptor inside a living body after weeks of exposure is a separate question. Biology adds time, and time can change what a signal means.</p>
That suggests a second reading. Maybe a receptor stimulated hard and continuously eventually stops responding, so a strong agonist ends up acting a lot like an antagonist, and the two drugs converge because the cell treats them about the same. Or maybe GIP affects several tissues in different ways, and each drug happens to move the one that matters for weight, from opposite sides. The sources do not choose between these. They call it “unresolved,” and I will leave it there too.</p>
I find this genuinely funny (in the way scientists probably do not enjoy). Picture the program meeting. “Hey team, good news, the antagonist works.” “Great, so the agonist was wrong?” “No, the agonist also works.” “So what does GIP do?” “Yes.”</p>

Why bolt a peptide onto an antibody</h2>
The point is the calendar. Incretin drug development has been a long effort to make doses last longer, from hours to days to a week (the site has a whole piece on half-life engineering). Peptides on their own get cleared fairly fast. Antibodies are large and are generally cleared much more slowly, so attaching the peptide to one is a way of letting it stay in circulation longer. Hence the expectation of monthly rather than weekly dosing. The sources here do not give the actual schedule tested, so treat the monthly framing as the design goal, not a reported result.</p>
To be fair, this is not the only route to convenience. A whole other branch of the pipeline is pursuing oral pills. Orforglipron, Lilly’s small-molecule pill, is the first oral small-molecule GLP-1 agonist to finish a phase 3 trial. In ATTAIN-1, a 72-week trial of 3,127 patients, it produced weight loss of 7.5%, 8.4% and 11.2% at 6, 12 and 36 mg, versus 2.1% on placebo. AstraZeneca’s elecoglipron reached up to 10.5% at week 26 in phase 2. A review of GLP-1 receptor biology says “dual and triple receptor agonists,” “biased agonist design,” and “oral formulations” are “the three major axes of next-generation incretin drug development.” An antibody you inject monthly does not fit neatly into any of them, which is a little awkward for anyone who likes tidy categories, and I write about drug pipelines, so that includes me.</p>
One side wants a daily pill. The other wants an injection a few times a year. Between them, you could build every possible schedule.</p>

What the phase 2 data can and cannot tell us here</h2>
This is where I would normally give you the phase 2 numbers. The sources available for this piece do not contain them. No percentages, no week counts, no dose arms. I am not going to fill that gap from memory, so whatever was reported in phase 2, this article does not settle it.</p>
What I can give is the benchmark any number will be compared against, which is very high. Tirzepatide: about 20% in phase 3. Retatrutide: up to 28.7% at 68 weeks in phase 3. UBT251, a triple agonist from China, reached 19.7% after 24 weeks in phase 2, versus 2.0% on placebo. Novo Nordisk’s CagriSema reached 23% at 84 weeks and still failed its non-inferiority test against tirzepatide, which reached 25.5%. That last example shows how this market works. A drug can produce 23% weight loss and still be counted as a disappointment, because the comparison is to the competitor, not to placebo.</p>
I assume, then, that the question for maridebart cafraglutide is not whether it causes weight loss. It is how it stacks up in a comparison table against drugs dosed weekly or daily. If the weight loss is comparable to the competition, the schedule becomes the selling point. If the weight loss falls short, the schedule becomes an explanation for why.</p>
Here is a deliberately silly scenario to show how far the logic goes. Say every company keeps extending dosing intervals: weekly, then monthly, then quarterly. Eventually someone puts a once-a-year obesity antibody in a slide deck, and the main clinical obstacle is that trial participants forget which year it is. Analysts start modeling adherence on a decade basis. That is where the incentive points, anyway.</p>

Both roads, same place</h2>
Put the two versions side by side. The simple version activates GIP and GLP-1 with one peptide and gets about 20% weight loss. The sophisticated version blocks GIP with an antibody, adds GLP-1 peptides, aims for monthly dosing, and arrives at the same basic claim: additive weight loss over GLP-1 alone. The longer road required a new modality and a contrary theory of GIP. It reached the same result, and then left the theory of GIP less clear than before.</p>
Basically, Amgen may succeed commercially regardless of which reading of the paradox turns out to be correct, since a monthly drug sells on the schedule, and GIP biology may stay unexplained for a long time while both molecules are on the market.</p>

Oral GLP-1s: Pills Made From Small Molecules vs Peptides

2026-11-01T00:00:00+00:00

The drugs that made this corner of medicine famous are made of roughly the same stuff as lunch, and for most of their history that meant they came in a needle. A paper on the structural biology of these drugs puts it flatly: “Currently approved GLP-1R agonists are peptide-based.” A peptide is a chain of amino acids, and your digestive system is a machine whose whole purpose is cutting chains of amino acids into pieces. Swallowing one is a bit like mailing a letter through a shredder.</p>

So there are two ways to make an oral GLP-1. You can keep the peptide and surround it with enough formulation chemistry (absorption enhancers, coatings, and so on) that some of it survives the trip and gets into the blood. Or you can drop the peptide altogether and build a small molecule, a different class of chemical, that still switches on the GLP-1 receptor. The second route now has its first Phase 3 success, Eli Lilly’s orforglipron, and a review article describes it in one sentence that holds the whole story if you read it slowly enough: “Orforglipron is an oral small-molecule, non-peptide GLP-1 receptor agonist developed by Eli Lilly.”</p>

What one sentence about orforglipron is actually claiming</h2>
I am going to read that sentence the way a lawyer reads an indemnification clause. (This is the kind of thing I enjoy more than is socially reasonable.) It has five working parts: “oral,” “small-molecule,” “non-peptide,” “GLP-1 receptor agonist,” and “developed by Eli Lilly.” Each one is doing real work. Two of them look redundant and are not.</p>
Take “oral” first, with appropriate solemnity. For purposes of this analysis, a drug is “oral” if it (a) enters the body through the mouth and (b) is still a functioning drug when it reaches somewhere useful. Both limbs are required. Plenty of things satisfy limb (a). Limb (b) is where peptides fail.</p>

Why an oral GLP-1 peptide is so hard to make</h2>
Tirzepatide, for instance, is a “39-amino-acid synthetic peptide.” That is a small protein. Well, more precisely, it is a short chain of the same building blocks your stomach and intestine spend all day producing from food, so in some sense a peptide drug is a molecule assembled from exactly the pieces digestion is designed to leave behind. The body does not hold it in any special regard. It gets digested like everything else.</p>
Here is a scenario, entirely made up, that shows the problem. Suppose you want a steak to reach your bloodstream intact. You coat it in something acid-resistant. Then you add a chemical that briefly makes the gut wall more permeable, so a whole steak can squeeze through. Then you discover only a tiny fraction gets through, so you swallow a much larger steak every morning, on an empty stomach, with precisely measured water, and wait before breakfast. Eventually you are running a small logistics company in your own esophagus. That is a caricature of the absorption-enhancer route, but only a caricature.</p>
And it can work. Novo Nordisk’s amycretin, a peptide that hits both GLP-1 and amylin receptors, has been tested as a pill: in a phase 1 trial, the group assigned 100 mg per day of oral amycretin lost a mean 13.1% of body weight versus 1.2% on placebo after 12 weeks. A 2026 review lists “oral peptide formulations” among the approaches still in clinical evaluation. What the facts in front of me do not settle is how much of a swallowed peptide actually gets absorbed, or how that compares with the small-molecule route. I don’t know, and I would rather say so than guess.</p>

What “small-molecule, non-peptide” means at the receptor</h2>
You might read “small-molecule, non-peptide” as saying the same thing twice, the way contracts say “null and void.” It is not quite that. “Small-molecule” is about size and how the thing gets made. “Non-peptide” is a promise about what it is not: not a chain of amino acids, and so not something the gut knows how to dismantle on sight. Most of the oral problem goes away inside those two words.</p>
The trouble moves to the receptor. The GLP-1 receptor belongs to a family that, per one structural review, follows “a two-step model for peptide binding and receptor activation.” The hormone’s tail end grabs the receptor’s outer domain, and its front end reaches into the transmembrane core and sends the signal. A cryo-EM study describes the GLP-1 peptide as “clasped” between those two parts, further stabilized by the receptor’s extracellular loops. The receptor evolved to be held by a long, floppy peptide at two points at once.</p>
A small molecule has no tail to grab with. It has to turn the switch without the handle. It is Indiana Jones swapping the golden idol for a bag of sand, except the goal is for the pedestal to notice and react exactly as if the idol were still there. You can picture the meeting where this started:</p>
“The hormone works great. It just gets digested.”</p>
“Okay. What if it weren’t a hormone?”</p>
The proof of concept came from a compound called LY3502970 (also known as OWL833), which a structural paper calls “a nonpeptide GLP-1R agonist with a pharmacokinetic profile favorable for oral administration.” Taken by mouth, it lowered glucose in mice engineered to carry the human GLP-1 receptor. Mice are not people. (This is the most repeated sentence in biomedicine, and it keeps being true.) But the switch turned.</p>

What “GLP-1 receptor agonist developed by Eli Lilly” commits to</h2>
“GLP-1 receptor agonist” is the functional claim: the molecule activates the receptor, whatever it looks like. That is the part that has to be shown in humans, and it has been. Lilly says orforglipron is “the first oral small-molecule GLP-1 receptor agonist to successfully complete a Phase 3 trial,” with HbA1c falling by an average of 1.3% to 1.6% across doses. Note how many qualifiers sit in that claim: oral, small-molecule, Phase 3. Each one narrows the field it was first in. (That is how firsts generally work in pharma, and I guess also in Little League.)</p>
Then “developed by Eli Lilly,” the most boring clause, which is of course where the business lives. Lilly positions orforglipron as potentially the first oral GLP-1 receptor agonist approved specifically for obesity. “Specifically for obesity” is another careful qualifier. And “developed” is the kind of word that, in a drug’s biography, can cover anything from conceiving the molecule at the bench to spotting someone else’s very promising compound early (a compound with two names, say, is sometimes just a compound with two names). I suppose all the clause strictly promises is whose name is on the trials.</p>

Who else is taking the small-molecule route</h2>
Look, a sentence that begins “the first” implies a second. HRS-7535 is another oral small-molecule GLP-1 receptor agonist that showed efficacy in a multicenter phase 2 trial in type 2 diabetes patients not controlled on metformin and SGLT2 inhibitors. Aleniglipron is one in development for obesity, with phase data published by Rosenstock and colleagues in Nature Medicine in 2026. The field site’s pipeline page has the full roster; the point here is just that the non-peptide trick has been reproduced.</p>
It is also spreading past GLP-1. Structure Therapeutics has ACCG-2671, an oral small molecule that binds the amylin and calcitonin receptors and produced dose-dependent weight loss in obese rats, with additive effects alongside semaglutide. Amylin is another peptide hormone, so the same logic applies: if the peptide cannot survive the stomach, build something that is not a peptide and that the receptor cannot tell apart.</p>
Which brings us back to the clause-by-clause reading. “Oral” was the goal, and “small-molecule, non-peptide” was how you get there. Put the two together and the sentence quietly says something strange. The leading oral version of a gut hormone drug is the one that contains none of the gut hormone.</p>

Orforglipron: The Small-Molecule GLP-1 Pill

2026-11-01T00:00:00+00:00

I spent part of this week trying to understand how you open a very specific biological lock with a key that looks nothing like the key, and the answer, as far as anyone has published it, is “carefully.” The lock is the GLP-1 receptor. For years the only keys anyone sold were copies of the original hormone, long chains of amino acids that have to be injected. Then Eli Lilly made one that is a pill.</p>

That pill is orforglipron. In the words of one review, “Orforglipron is an oral small-molecule, non-peptide GLP-1 receptor agonist developed by Eli Lilly.” Lilly says it is “the first oral small-molecule GLP-1 receptor agonist to successfully complete a Phase 3 trial,” and in that trial it lowered HbA1c (a three-month average of blood sugar) by an average of 1.3% to 1.6% across doses. Lilly is positioning it as potentially the first oral GLP-1 receptor agonist approved specifically for obesity. So there are two ways to activate this receptor. One is obvious and one is elaborate, and they end up in roughly the same place.</p>

The dumb version: just use the hormone</h2>
The dumb version goes like this. Your gut makes a hormone called GLP-1. It docks on the GLP-1 receptor, and then good things happen: appetite drops, the stomach empties more slowly, and the pancreas releases insulin when blood sugar is high. So you make more of the hormone, tweak it so it lasts longer, and inject it. (Why it needed tweaking is its own long story, and another article on this site tells it.)</p>
I call this “dumb” with real affection. It works. GLP-1 receptor agonists achieve approximately 6% to 15% weight loss in clinical trials, and they reduce major cardiovascular events. Tirzepatide, a 39-amino-acid synthetic peptide that also hits the GIP receptor, does better. The original-key strategy has been extremely good to everyone involved.</p>
The cryo-EM structure of the activated receptor shows why the original key fits so well. The GLP-1 peptide is “clasped between the N-terminal domain and the transmembrane core of the receptor.” Basically the receptor has a big outer arm and a core buried in the cell membrane. The peptide is long enough to touch both at once, and the receptor hugs it. The GLP-1 receptor is a class B G protein-coupled receptor, and class B receptors are known for wanting a big hormone with a lot of surface to grab.</p>
The problem with the dumb version is that a long peptide is a bad thing to swallow. Your digestive system treats a protein chain as lunch (which, from its point of view, it is). So the dumb version mostly comes with a needle.</p>

The sophisticated version: how a non-peptide activates the GLP-1 receptor</h2>
The sophisticated version starts with a medicinal chemist in a meeting saying something like “hey, what if it’s just not a peptide?” Everyone nods. Then they spend years on it.</p>
Here is the mechanism in plain words. A small chemical, built nothing like the hormone, slips into the receptor, sits somewhere it can reach, and nudges the receptor into the same shape the hormone would. The receptor cannot tell the difference, or at least does not object. This is called non-peptide agonism, and orforglipron is the commercially serious example of it.</p>
The shape matters more than the key. When the GLP-1 receptor activates, conformational changes in its transmembrane domain put “a sharp kink in the middle of transmembrane helix 6,” in the words of the cryo-EM structure paper. That kink is what lets the G protein bind on the inside of the cell and start the signal. The receptor doesn’t sort of care what caused the kink. It cares that the kink happened.</p>
A peptide gets there by draping itself across a large surface. Work on peptide dual agonists shows how much territory is involved: the middle of those peptides recognizes extracellular loops 1 and 2 and the top of transmembrane helix 1, and the first three residues reach into a deep binding pocket where small differences decide which receptor gets activated. A small molecule cannot cover all of that. It has to find a smaller set of contacts that produce the same kink. Exactly how orforglipron does this, contact by contact, is not something the sources here settle, so I won’t pretend they do.</p>
The peptide and the receptor have a long, committed, fully documented relationship. The small molecule’s arrangement with the receptor is blurrier, and everyone involved seems happy to keep it that way as long as the signal comes through.</p>

What the orforglipron Phase 3 trials showed</h2>
The headline is that this went fine. That is understating it on purpose. A pill that activates a receptor famous for needing a big hormone made it through a Phase 3 trial, lowered HbA1c by 1.3% to 1.6% on average, and, according to Lilly, showed “a safety profile consistent with injectable GLP-1 medicines.” That last phrase is the whole sophisticated version in one line. The elaborate road was built in order to arrive at “consistent with injectable.”</p>
The obesity program is called ATTAIN, and researchers are already publishing post hoc analyses of it. One looks at adults with a body mass index of 27 to under 30 who have adiposity-related complications, from ATTAIN-1. Another pools ATTAIN-1 and ATTAIN-2 to look at patients 65 and older, with or without type 2 diabetes. Post hoc analyses are a good sign of where a drug is in its life. Nobody slices the data by age bracket unless the main result was worth slicing.</p>
What I can’t give you, from the sources in front of me, is the headline ATTAIN weight-loss number, and I’m not going to invent one. The fair comparison point is the class: approximately 6% to 15% for GLP-1 receptor agonists generally. Where orforglipron lands in that range is the question that decides whether it is “the pill version” or “a pill that is also pretty good.” Those are different businesses.</p>
It is also not alone. A 2024 systematic review counted 14 ongoing Phase 3 obesity trials, orforglipron’s among them, next to retatrutide, CagriSema, survodutide and others. Behind it, HRS-7535 has shown efficacy in a Phase 2 diabetes trial, aleniglipron has Phase data published in Nature Medicine in 2026, and Structure Therapeutics has an oral small molecule called ACCG-2671 that goes after the amylin and calcitonin receptors instead. Once one company shows a lock can be picked, the lockpicking catalogs get thicker.</p>

Why the manufacturing story might be the real story</h2>
I assume most of the excitement about orforglipron in boardrooms is not about receptor kinks. (I write a newsletter about molecules I could not draw with a gun to my head, so I respect people who can.) It is about making the stuff.</p>
This part is mostly reasoning, not reported fact, so take it as that. A peptide drug is a chain of amino acids (39 of them, in tirzepatide’s case) that has to be assembled in order and then gets injected. A small molecule is a compact chemical. The general hope with small molecules is that they are easier to make at scale, easier to ship and easier to take. The sources here give no cost figures, no capacity numbers and no price, so how big that advantage is for orforglipron is not settled.</p>
Here is a scenario I made up, to show the shape of the problem. Imagine demand for incretin drugs keeps growing until every peptide production line on earth runs around the clock. Then a company proposes a new line just for one ingredient. Then a second. Then someone suggests moving amino acid suppliers next door to the plants, then putting the plants next to the pharmacies, then putting a small peptide reactor in every clinic, then in every kitchen, next to the toaster. At some point, presumably, someone at the back of the room says “or it could be a tablet,” and the room goes quiet.</p>
To be fair, the pill doesn’t make the peptides obsolete. The multi-agonists (tirzepatide, retatrutide, the amylin combinations) are where the biggest weight-loss numbers come from, and the sources describe oral formulations as just one of three major directions in incretin drug design, next to multi-receptor agonists and biased agonists. It’s fine. A field can have more than one good idea at once. I mean, the movie heist always needs both a guy who cracks the safe and a guy who drives the van.</p>

Where the two versions meet</h2>
So you have the dumb version: copy the hormone, protect it, inject it, and let the receptor clasp it. And the sophisticated version: throw out the hormone entirely, design a compact chemical from scratch, find a way to bend helix 6 without the hormone’s long reach, make it survive the stomach, and run it through Phase 3. The second road is much longer.</p>
It ends in the same place. The receptor gets its kink. The G protein binds. Blood sugar comes down by an amount that is “consistent with injectable” in safety terms and in the familiar range on efficacy. All that chemistry, and the measure of success is resembling the thing you were replacing.</p>
The lock is the same lock it always was. It just turns out you can open it with something you swallow.</p>

Retatrutide Trial Results, Read Carefully

2026-11-01T00:00:00+00:00

If you are Eli Lilly and you own a drug that makes people lose a startling amount of weight, your problem is not the drug. Your problem is that every result leaves the building as one number, and the number travels without the paragraph that explained it. So here are the retatrutide results as plainly as the facts allow. In phase 2, a 48-week study in adults with obesity but without type 2 diabetes (weekly doses from 1 mg to 12 mg, average starting BMI of 37.4) sits behind the figure that a review in Annals of Internal Medicine put at the top of its table: 24.2% weight loss at 12 mg weekly, ahead of tirzepatide at 17.8% and injected semaglutide at 13.9%.</p>

In phase 3, TRIUMPH-1 (80 weeks, adults with obesity or overweight plus at least one weight-related condition, no diabetes) reported its topline on May 21, 2026, under an AJMC headline promising “Up to 30.3% Average Weight Loss.” By week 80, 37.5% of participants who started with class 3 obesity (BMI of 40 or more) had a BMI below 30 on the 12 mg dose. TRIUMPH-2, in adults with obesity and type 2 diabetes, reached up to 20.8%. There are also inflammation numbers and a liver story, which we will get to, and one important thing the facts here do not settle, which we will also get to.</p>

The dumb version of reading a trial</h2>
The dumb version goes like this. You see “30.3%” in a headline. You conclude that people on retatrutide lose 30.3% of their weight. You tell a friend at dinner. Done.</p>
This is a perfectly reasonable thing for a human to do. It is also what the headline was built for. (Headlines are not built to be footnoted.) And here is the weird part: the dumb version gets you to roughly the right conclusion, which is that this drug causes a very large amount of weight loss, more than the drugs that came before it. Hold onto that, because the sophisticated version is going to spend a lot of words arriving at the same spot.</p>

The sophisticated version, or what endpoints mean</h2>
A trial is designed before anyone takes a dose, and the design says in advance what will count as the answer. That pre-declared answer is the primary endpoint. For obesity trials it is typically the average percent change in body weight from the start of the trial to a fixed week, compared against people who got a placebo injection. Everything else (the share of people who crossed some threshold, blood markers, liver fat, etc.) is a secondary endpoint or an exploratory one, and the further down that list you go, the less weight the trial’s statistics were built to carry.</p>
Then there is the official description of the design. The Lancet paper on the phase 3 diabetes trial calls TRIUMPH-2 “a double-blind, parallel-group, randomised, placebo-controlled, phase 3 trial.” Translated: people were sorted by coin flip into separate groups at the same time, some got fake shots, and nobody in the room knew who got what. That sentence is doing most of the work of making a number believable.</p>
Now look at “up to.” “Up to 30.3%” means the best-performing dose arm, on average. Other doses lost less. The average also contains people who lost much more and people who lost much less. And a percentage is a percentage of where you started, so a person starting at BMI 45 and a person starting at BMI 32 can post the same percent and end in very different places. That is why the 37.5% figure is interesting: it is not a percent of weight, it is a percent of people who crossed a line.</p>

What the phase 2 retatrutide results actually measured</h2>
The number I keep coming back to is 24.2%.</p>
A 2024 systematic review found that completed phase 2 trials of incretin-based obesity drugs showed mean weight loss ranging from 7.4% to 24.2%. So 24.2% is the ceiling of the entire field’s phase 2 work at that point, the single highest mean among every incretin molecule that had finished a mid-stage trial. And then the Annals review, pooling 26 randomized trials and 15,491 adults without diabetes, lists retatrutide at 12 mg weekly at exactly 24.2%. Presumably that is the same phase 2 number showing up in two places (the facts I am working from do not say so outright, and I am not going to pretend they do). Either way, one dose of one molecule defined the upper edge of a whole class. That is a lot of responsibility for a decimal.</p>
On the other hand, the phase 2 obesity study was 48 weeks long and TRIUMPH-1 ran 80 weeks. Longer trials give a drug more time to keep working, which is part of how a 24.2% becomes an “up to 30.3%.” Comparing those two numbers as though they were the same measurement is how you end up very confident and slightly wrong.</p>

Diabetes, inflammation and the liver</h2>
There were two phase 2 trials, one in obesity without diabetes (Study 2) and one in type 2 diabetes (Study 1). Researchers later ran what the paper calls “a post-hoc analysis of two phase 2 retatrutide trials” that “assessed lipoprotein and inflammatory biomarkers.” Post-hoc means after the fact, which in medicine is a respectable way of going back to the data for a second look and, in most other areas of life, is how you end up explaining yourself to a group chat.</p>
What they found: in Study 2, retatrutide cut high-sensitivity C-reactive protein by 54.8% and interleukin-6 by 29.6% versus placebo. In Study 1, the diabetes population, those reductions were not statistically significant. That’s fine, and it is also the sort of detail a headline drops. Not significant does not mean the markers went up. It means the trial could not rule out chance.</p>
On diabetes more broadly, Lilly’s own release on its first phase 3 type 2 diabetes trial, TRANSCEND-T2D-1, says retatrutide “demonstrated significant reductions in A1C and weight.” The specific A1C figure is not in the material I have, so I will leave it there. TRIUMPH-2 reached up to 20.8% weight loss in people with both obesity and diabetes, which is lower than the non-diabetes trials. People with diabetes tend to lose less weight on these drugs; tirzepatide’s own trial program has the same split between SURMOUNT and SURPASS.</p>
The liver is where I have to be honest about the limits. A review of glucagon signalling says that in early trials, retatrutide, survodutide and mazdutide each showed “substantial efficacy for weight loss in people with obesity while improving liver health in those with MASLD.” The actual liver substudy numbers (fat fraction, how many people normalized, etc.) are not in the facts I was handed. I feel like the responsible move for a guy who writes about other people’s spreadsheets is to say that and stop.</p>

Why everyone reads it the way they do</h2>
Everyone in this story is behaving sensibly. Lilly announces the best dose because the best dose is the news, and its job is to tell investors and doctors what the drug can do. Investigators report pre-declared endpoints and flag post-hoc ones because that is what keeps them honest. Journalists lead with the biggest number because a headline that said “Mean Percent Change From Baseline in the Highest Dose Arm” would be read by about four people (I would be one of them). And readers take the headline number because they have jobs.</p>
Here, as an illustration I am inventing, is how it goes wrong. A reader sees 30.3% and assumes tirzepatide is now obsolete. She sees 17.8% for tirzepatide in the Annals review and 19.5% and 20.9% in SURMOUNT-1, and compares them all to 30.3%, mixing trial lengths, populations and doses. Her brother-in-law then compares 30.3% to orforglipron’s 11.2% in ATTAIN-1 and announces that pills are over. Someone else notices UBT251 hit 19.7% in only 24 weeks and extrapolates to 80 weeks, and by Thanksgiving the family has a drug that makes people disappear entirely. A statistician somewhere says, “guys, these are different trials,” and is not invited back.</p>
This is a bit like comparing a marathon time to a half-marathon time and declaring the half-marathoner faster. Correct arithmetic, wrong race.</p>

Where the long road ends</h2>
The proper fix for cross-trial comparison is a head-to-head trial, and there is one: TRIUMPH-5, retatrutide versus tirzepatide, with an estimated primary completion in November 2026. Results from that trial are not among the facts here, so whether the gap holds when the two drugs share a protocol is not settled.</p>
Anyway, after all the endpoints, estimands-in-spirit, dose arms, post-hoc caveats and population splits, the sophisticated version does reach a conclusion. A 2026 review says triple agonists like retatrutide “have exhibited unprecedented weight-loss efficacy in clinical trials.” Which is what the guy at dinner said, with more syllables. The point is that the long road and the short road land in the same parking lot; the long road just knows which parking space, and that diabetes patients park a few spaces further away.</p>
At this rate the most careful possible reading of retatrutide results is simply the headline, delivered eighty weeks later with a confidence interval.</p>

Retatrutide: The Triple Agonist Everyone Is Watching

2026-11-01T00:00:00+00:00

One review of drugs for chronic kidney disease describes retatrutide in seven words: “Retatrutide is a triple GLP-1/GIP/glucagon receptor agonist.” There is no second clause, no hedge and no dose, and it is also, more or less, the whole drug. If you read it slowly enough, it tells you what Eli Lilly built, how it is supposed to work, and why its phase 3 results have made it the molecule that people in obesity drug development keep refreshing their browsers about.</p>

So, plainly: retatrutide is an experimental drug from Eli Lilly that activates three hormone receptors at once, dosed weekly in its trials. In Lilly’s phase 3 TRIUMPH-1 trial, the 12 mg dose produced a mean weight loss of 28.3% at 80 weeks by one method of counting, and all three doses tested met their primary endpoints. Whether and when it gets approved is a separate question, which another article on this site takes up. What follows is a close reading of that seven-word sentence, one word at a time, as if it were a contract someone might later sue over.</p>

What “retatrutide is a” commits Lilly to</h2>
Start with the article. “A” agonist, singular. That matters more than it looks. Some of the competition is two drugs in one syringe (CagriSema pairs a GLP-1 drug with an amylin drug), but the sentence promises one molecule doing all three jobs. The sources here don’t give retatrutide’s amino acid sequence, so I won’t pretend to. For scale, its older sibling tirzepatide is, per one cardiovascular review, a “39-amino-acid synthetic peptide” that hits two receptors and earned the nickname “twincretin.”</p>
The nickname for retatrutide would presumably be “tricretin,” except that one of its three targets isn’t an incretin at all. We will get there.</p>

What a receptor agonist is, in plain words</h2>
Here is the mechanism with the jargon removed. Your cells have little switches on their surfaces. Hormones float by and flip them. A drug can be built to look enough like the hormone that it flips the switch too, and to hang around for a week instead of a few minutes (the half-life engineering is its own article). Retatrutide is one key cut to fit three different locks.</p>
The official name for a key that turns the lock, rather than just jamming it, is “receptor agonist.” The opposite is an antagonist. That is basically the entire vocabulary.</p>
Two of the three locks are GLP-1 and GIP, the gut hormones that tell the body a meal has arrived (the incretin explainer on this site covers them properly). Tirzepatide already hits both. The third lock is glucagon, and this is where the sentence gets interesting, because glucagon’s best-known job is raising blood sugar. In a drug that is also tested in people with type 2 diabetes, that is sort of like hiring an arsonist for the fire department.</p>
I assume the meeting went something like: “Hey, what if we add the hormone that does the opposite of what we want?” “For energy expenditure.” “Fine, but it needs supervision.”</p>
That is, more or less, the published rationale. A 2026 review of glucagon signaling notes that mazdutide, survodutide and retatrutide are each glucagon-based multi-agonists that “also incorporate GLP-1 receptor-activating moieties to counteract glucagon’s hyperglycaemic effects.” An article headlined “Novo Nordisk’s triple agonist delivers up to 19.7% weight loss” puts it as a trade: “the dual incretin activity of GLP-1 and GIP offsets glucagon’s hyperglycemic effects in triple agonists while retaining energy expenditure benefits.”</p>
So glucagon gets into the molecule, but only chaperoned. It is allowed to do the part where the body burns more energy, and two incretins stand next to it to make sure it does not do the other thing. What exactly the energy part is remains not settled. One line of research proposes that these dual and triple agonists drive “adaptive thermogenesis” (heat production in brown and beige fat) by changing amino acid metabolism there. “Proposed” is the operative word.</p>

“Triple,” and who else is counting to three</h2>
The word “triple” is doing marketing work, but it is also accurate, and retatrutide is not alone. That Novo Nordisk article calls retatrutide “the most advanced triple agonist globally,” while reporting on UBT251, another triple GLP-1/GIP/glucagon peptide, which showed weight loss of 13.6% to 19.7% versus 2.0% for placebo in a 24-week phase 2 trial of 205 adults. A 2024 systematic review counted 14 ongoing phase 3 trials of obesity drugs, retatrutide among them. One 2026 review lists dual and triple agonists as one of “the three major axes” of next-generation incretin development, alongside biased agonists and pills.</p>
The obvious next move is a fourth receptor, and then a fifth. To be clear, I am making this up: some company announces a quadruple agonist, a rival answers with a quintuple, and within a decade the leading candidate is a single peptide that binds every receptor in the human body, at which point it is less a drug than a second, more agreeable copy of the patient. It’s fine. Nobody is actually proposing this. The fantasy football logic of drafting every star onto one roster runs into the problem that each extra receptor is another thing that can go wrong.</p>
And things do cost something. A network meta-analysis of 14 trials of glucagon-receptor agonists found retatrutide produced the largest weight reduction versus placebo (a mean difference of 13.44 kg) and the largest HbA1c reduction, but it was also among the agents with “comparatively lower tolerability,” while mazdutide had the most favorable profile. Three locks, more side doors.</p>
On phase 2: the sources here do not lay out retatrutide’s phase 2 trial by itself, so I won’t invent its numbers. The closest thing is a review in Annals of Internal Medicine pooling 26 randomized trials of 15,491 adults without diabetes, which found retatrutide led at 24.2% weight loss on 12 mg weekly, ahead of tirzepatide at 17.8% and injectable semaglutide at 13.9%. Which trials fed that figure isn’t specified in what I have.</p>

What the retatrutide TRIUMPH phase 3 trials have shown</h2>
The phase 3 obesity program is called TRIUMPH, which is a confident name to give a trial before it reads out. It worked out.</p>
TRIUMPH-1 (NCT05929066) reported topline results on May 21, 2026. Participants started at an average of 248.5 lb. On the 12 mg dose, the mean loss at 80 weeks was 70.3 lb, or 28.3%, across 2,339 people by what is called the efficacy estimand. That is a bit more than a quarter of a person.</p>
The 9 mg dose produced 25.9%. The 4 mg dose produced 19.0%. On 12 mg, 45.3% of participants lost 30% or more of their body weight, and 65.3% got their BMI below 30. Among people who entered with class 3 obesity (BMI 40 or higher), 37.5% reached a BMI below 30 on 12 mg. In a prespecified blinded extension for people with BMI of at least 35, those on 12 mg reached 30.3% by week 104.</p>
There are two ways of counting in these trials, and they give different answers. By the treatment-regimen estimand, one pipeline tracker puts the TRIUMPH-1 figure at “up to 25%.” Both numbers are real; they answer slightly different questions about who gets counted how. Headlines tend to pick the bigger one. (Headlines are not peer-reviewed.) A separate report mentions phase 3 data of “up to 28.7% weight loss at 68 weeks,” and the sources here don’t reconcile that with the 80-week figures.</p>
TRIUMPH-2 (NCT05929079), in people with obesity and type 2 diabetes, and TRIUMPH-3, in people with severe obesity and established cardiovascular disease, both reported positive toplines on July 23, 2026: up to 20.8% and 22.6% weight loss, respectively. People with diabetes tend to lose less on these drugs, so the lower number there is about what you’d expect. Separately, TRANSCEND-T2D-1, a 40-week diabetes trial of 537 people, showed HbA1c drops of 1.69 to 1.94 points against 0.81 for placebo, and weight loss of 11.5% to 15.3% against 2.6%.</p>

Why the next trial pits Lilly against Lilly</h2>
Which brings us to TRIUMPH-5 (NCT06662383), a head-to-head trial of retatrutide against tirzepatide, with primary completion estimated for November 2026. That is this month.</p>
I mean, this is a strange trial to run. Both drugs belong to Lilly. Tirzepatide hit 19.5% and 20.9% at its two top doses in SURMOUNT-1, a different trial with different people, which is exactly why cross-trial comparisons are shaky and why a direct comparison is worth paying for. What is the good outcome here? Retatrutide wins, and Lilly has spent years telling everyone how great its other drug is. Tirzepatide holds up, and the third receptor looks like a lot of chemistry for a little extra. (The site’s comparison piece takes up whether glucagon is worth it.)</p>
Either way, Lilly learns something about Lilly.</p>
So here is the sentence again, with the one clause it was missing: retatrutide is a triple GLP-1/GIP/glucagon receptor agonist, currently being tested against a double one made by the same company. If you are the Lilly sales rep who spent three years explaining why two receptors is the right number, you had better start practicing the word “three.”</p>

Survodutide: The GLP-1/Glucagon Dual Aimed at the Liver

2026-11-01T00:00:00+00:00

Here is a small fact about survodutide: it is a weight-loss drug that works partly by switching on the receptor for glucagon, a hormone whose normal job is to raise blood sugar. Survodutide is a single peptide that activates both the GLP-1 receptor and the glucagon receptor. Boehringer Ingelheim is developing it for obesity and for fatty liver disease, which is why it keeps getting described as the dual agonist aimed at the liver.</p>

That is the plain answer, and the status is easy to state. A 2024 systematic review of obesity drugs counted 14 ongoing phase 3 trials and listed “mazdutide and survodutide (GLP-1/glucagon RAs)” among them. Survodutide’s first phase 3 topline results, from a trial called SYNCHRONIZE-1, were reported on April 28, 2026. The liver part rests on early trials in people with MASLD, the fatty-liver condition the program is built around, along with its more serious form, MASH. The rest of this post is about why anyone would design a drug this way. It is a strange design.</p>

Start with a drug that does one thing</h2>
Begin with the reasonable version. A GLP-1 drug imitates a gut hormone that tells your brain you have eaten, so you eat less. That works. (The site has a whole article on what an incretin is, so I will skip the history.) Then someone added a second hormone, GIP, and got tirzepatide, which produced mean weight loss of 19.5% and 20.9% at its 10mg and 15mg doses in the SURMOUNT-1 phase 3 trial. Two hormones, both mostly about appetite and insulin. Still reasonable.</p>
Now take the next step. Add glucagon.</p>
Here is the mechanism in very plain words. You put a hormone that pushes blood sugar up into the same molecule as a hormone that pushes it down, and you hope the up and the down cancel while the other effects remain. The official name for this is dual GLP-1/glucagon receptor agonism. A 2025 review of glucagon signalling describes survodutide, mazdutide and retatrutide as “GCGR-based multi-agonists that also incorporate GLP-1 receptor-activating moieties to counteract glucagon’s hyperglycaemic effects.” Put differently, the GLP-1 half is partly there to clean up after the glucagon half.</p>
The body does not normally run things this way. In the old rat-cell research, GLP-1 is proposed to suppress glucagon release through a middleman: it triggers somatostatin, which “in turn suppresses exocytosis in alpha-cells,” in that paper’s words. So nature uses GLP-1 to turn glucagon down, and survodutide asks both of them to work at full volume at the same time. I feel like this meeting went something like this (I invented it): “Hey guys, what if the molecule also did the thing the body uses GLP-1 to stop?” Then everyone looked at the liver data and decided it was not dumb.</p>

Why glucagon is the hormone you send to the liver</h2>
It is hereby stipulated, for purposes of this discussion and without prejudice to any future article, that a hormone which raises blood sugar is an unusual ingredient for a family of drugs that is judged, in part, by how much it lowers HbA1c. The case for including it anyway rests on where glucagon works and what it does when it arrives.</p>
On where: the glucagon review says the receptor “is expressed in the liver and kidney, and to a lesser extent in various other tissues,” which is how you would describe a receptor that has one serious relationship and keeps a few others discreet. The liver is the serious one. On what: glucagon promotes the breakdown of liver glycogen, and it “stimulates lipolysis and mitochondrial fat oxidation in the liver.” A fatty liver is a liver holding too much fat, and here is a hormone that tells the liver to burn its fat. The logic is not complicated. That’s fine.</p>
There is also a whole-body version. A review of next-generation dual agonists says GLP-1/glucagon agonism “increases energy expenditure by stimulating fat oxidation and glucose production, distinguishing it from the appetite-focused GLP-1/GIP approach.” Tirzepatide gets you to eat less. A glucagon dual is meant to get you to eat less and also burn more. That is the pitch.</p>

How far the escalation goes, and how far it has gone</h2>
Push the hypothetical one step further. If a drug can make the liver burn more fat, why not the rest of you? Then push it again: a drug that turns your body into a small furnace, so that weight loss arrives partly as heat. (This part is made up.) In the endpoint version, a patient on the drug heats their own apartment, the utility bill falls, and the trial’s key secondary endpoint is measured in BTUs. Somebody files a patent on the thermostat.</p>
The real world is further along this road than you might expect. A recent paper on amino acids and thermogenesis reports that dual and triple GLP-1/GIP/glucagon agonists “promote thermogenic-like amino acid profiles in BAT with robust heat production,” where BAT is brown fat, the kind that burns energy to make heat. The same authors propose that these drugs trigger “sympathetic activation and adaptive thermogenesis” in brown and beige fat. Note “proposed.” That is a mechanism hypothesis about the class, mostly from lab work, not a measurement of survodutide in people. Nobody has shown the apartment-heating thing. Yet.</p>
The chemistry of getting one peptide to fit two receptors is its own small spectacle. Cryo-EM studies of three other GLP-1/glucagon duals (cotadutide, SAR425899 and something just called peptide 15) found that receptor selectivity depends on how the first three amino acids sit in the deep binding pocket, and that interaction with a part of the receptor called extracellular loop 1 “plays an important role in executing dual agonism.” (I write about drug pipelines for a living, which mostly means reading the phrase “extracellular loop 1” and nodding in a way I hope looks informed.) Those structures are not survodutide’s. The principle carries over: you are tuning one key to turn two locks by different amounts, and the balance is the whole product.</p>

What survodutide’s MASH and obesity data show so far</h2>
Now the numbers, and the gaps where the numbers should be. The glucagon review says that in early clinical trials, mazdutide, survodutide and retatrutide “each demonstrated substantial efficacy for weight loss in people with obesity while improving liver health in those with MASLD.” That is a summary, not a result table. The specific readouts from survodutide’s phase 2 MASH trial (how many patients saw their liver disease resolve, how much scarring improved, at which doses) are not in the sources I am working from, so I will not state them. That part is not settled here.</p>
On weight, the cleanest figure comes from a network meta-analysis of glucagon receptor agonists, which put survodutide’s mean weight reduction at -10.74 kg versus placebo, with a 95% confidence interval of -15.68 to -5.80. That interval is wide. Network meta-analyses stitch different trials together, so treat the figure as an estimate rather than a head-to-head result. It is also in kilograms, while most headlines quote percentages, which makes lining it up against tirzepatide’s 20.9% a matter of guesswork. Is a glucagon dual better than a GIP dual? Those numbers do not let you say.</p>
The phase 3 obesity program is the real test, and as of this writing the public record available to me holds only the date: SYNCHRONIZE-1 reported topline results on April 28, 2026. What those results said is not in my sources. Meanwhile the field has kept escalating. Retatrutide adds GIP on top of glucagon and GLP-1, and a newer triple, UBT251, posted -13.6% to -19.7% weight loss against -2.0% for placebo over 24 weeks in a phase 2 trial of 205 adults. Its makers say the GLP-1 and GIP activity offsets glucagon’s effect on blood sugar. Whether two balancing hormones beat one is the question the site’s triple-agonist pieces chase. Anyway.</p>
One more detail, since it is printed right on the paper. The 2025 glucagon review quoted throughout this post was “funded by Boehringer Ingelheim Pharmaceuticals, Inc., which is developing survodutide.” Disclosed, routine, how a lot of this stuff gets written, lol. By its sponsor’s own paperwork, then, survodutide is not really a new GLP-1 drug. It is a glucagon drug, and the GLP-1 is the chaperone.</p>

Tirzepatide vs Retatrutide: Is Adding Glucagon Worth It?

2026-11-01T00:00:00+00:00

Here is a small fact about the two most-discussed weight-loss molecules in the pipeline: as of today, no published trial has given them to the same people at the same time. Tirzepatide is a dual agonist that hits the GIP and GLP-1 receptors. Retatrutide is a triple agonist that hits those two plus the glucagon receptor. On the numbers that exist, retatrutide loses more weight. In its TRIUMPH-1 trial, the 12 mg dose produced 28.3% average weight loss at 80 weeks. In SURMOUNT-1, tirzepatide produced 19.5% at 10 mg and 20.9% at 15 mg.</p>

So the honest answer to tirzepatide vs retatrutide is that retatrutide looks bigger. The direction is probably real and the size is not settled. The head-to-head trial meant to settle it, TRIUMPH-5 (NCT06662383), has an estimated primary completion of November 2026. That is this month. The comparison everyone is making is, in some sense, a comparison of two different trials’ results, and the rest of this article is about why that is both useful and a little dumb.</p>

What glucagon is doing in a weight-loss drug</h2>
Adding glucagon is a strange choice on its face, because glucagon is the hormone that raises blood sugar. That is roughly the opposite of what the diabetes half of this field has spent decades trying to do. The drug designers’ answer is to pair it with GLP-1 activity. A review titled “Shared mechanistic pathways of glucagon signalling” says glucagon-based multi-agonists like retatrutide include GLP-1 receptor-activating pieces “to counteract glucagon’s hyperglycaemic effects.” You add the thing that raises blood sugar, and then you add the thing that cancels it, and you keep whatever else it does.</p>
What else it does, per the literature, is spend energy. GLP-1/glucagon agonism is described as increasing energy expenditure by stimulating fat oxidation, which distinguishes it from the more appetite-focused GLP-1/GIP approach that tirzepatide takes. Tirzepatide mostly makes you want less food. Glucagon, in theory, also makes the body burn more of what it has. (Why GIP helps at all is its own puzzle, since both stimulating and blocking the GIP receptor seem to add weight loss on top of GLP-1. A different article on this site gets that one.)</p>
There is a cost, at least in the data so far. A network meta-analysis of glucagon receptor agonists found that retatrutide showed the largest weight reduction against placebo (a mean difference of -13.44 kg) and the largest HbA1c reduction, but it and cotadutide “were associated with comparatively lower tolerability” than mazdutide. More receptors, more effects. Some of them you wanted.</p>

A tirzepatide vs retatrutide comparison you could trust, and then worse ones</h2>
Let’s build up from the good version. Step one: you take a few thousand similar people, randomly assign half to each drug, run them for the same number of weeks with the same diet counseling and the same measurement rules, and compare. That is a head-to-head randomized trial, and it is the only kind of comparison where the difference between two numbers is mostly the difference between two drugs. SURMOUNT-5 did this for tirzepatide against semaglutide, with 751 participants without diabetes. TRIUMPH-5 is doing it for retatrutide against tirzepatide. Fine.</p>
Step two: you run two separate trials, one per drug, each against placebo, in different years. The people are similar-ish. You compare the drug arms anyway. Step three: the trials are different lengths, so one drug got more weeks to work than the other. Step four: the trials enrolled different people (people being, inconveniently, the main ingredient). Step five: you pool 26 trials of 12 drugs into a meta-analysis and rank them (this is considered rigorous, and it mostly is, which is the annoying part). Step six, the absurd endpoint: you just compare the best number each drug has ever had printed next to its name, in any trial, at any dose, in anyone.</p>
This is a bit like comparing your commute to a coworker’s when they live farther away, drive a different road, and left the house at a different hour. You learn something. You do not learn whose car is faster. (Sports fans have the same argument about whether a hitter from one decade was better than a hitter from another, and it has never been resolved, and the stakes there are lower.)</p>
“Please don’t put these two in the same chart,” is a thing a trial statistician might say, right before someone puts them in the same chart. I write articles that put numbers from different documents next to each other for a living, so I am not throwing stones here.</p>

How far down that road the real numbers are</h2>
Pretty far, it turns out. Consider tirzepatide alone, the same molecule in different rooms. In SURMOUNT-1 it got 20.9% at 15 mg. In the SURMOUNT-5 subpopulation meeting Japanese obesity criteria, it got a -20.1% change at week 72. In CagriSema’s phase 3 trial it served as the comparator and got 25.5% at 84 weeks, while CagriSema got 23% and failed to show non-inferiority. Same drug. Several numbers.</p>
Retatrutide moves around too. TRIUMPH-1 enrolled people with a baseline average weight of 248.5 lb and a BMI of 40.0, ran 80 weeks, and reported 28.3% (70.3 lb) by the efficacy estimand, with 2,339 participants in that analysis. In TRANSCEND-T2D-1, which enrolled people with type 2 diabetes and ran 40 weeks, the 12 mg dose produced 15.3% weight loss. People with diabetes tend to lose less on these drugs, and 40 weeks is half of 80, so this is not a contradiction. It is just step four in action.</p>
Then there is step five. A review in Annals of Internal Medicine looked at 26 randomized trials involving 15,491 adults without diabetes and found retatrutide led at 24.2% at 12 mg, ahead of tirzepatide at 17.8% and subcutaneous semaglutide at 13.9%. Notice that retatrutide’s number there is lower than its TRIUMPH-1 number, and tirzepatide’s is lower than its SURMOUNT-1 number. Pooling pulls everyone toward the middle. The ranking held.</p>
So here is the question, and it has two readings. Retatrutide’s TRIUMPH-1 figure is about 7 points above tirzepatide’s best SURMOUNT-1 figure. One reading is that this is glucagon: the energy-expenditure mechanism working on top of appetite suppression, exactly as designed. The other reading is that TRIUMPH-1 enrolled heavier people, ran a long time, and reported the flattering estimand, and that tirzepatide in that same trial might have closed a chunk of the gap (its own 25.5% at 84 weeks suggests it can stretch). Both readings fit the published numbers. I don’t know which is closer. Neither does anyone outside the TRIUMPH-5 data room, I guess.</p>
The pooled-ranking world is also getting crowded. A 2024 systematic review counted 14 ongoing phase 3 obesity trials. UBT251, another triple GLP-1/GIP/glucagon agonist, showed -13.6% to -19.7% at 24 weeks in a phase 2 trial of 205 adults. A 2026 review on central appetite regulation and peripheral energy expenditure said glucagon-containing dual and triple agonists like retatrutide “have exhibited unprecedented weight-loss efficacy in clinical trials.” That is true, and also every one of those trials had its own patients, its own length and its own estimand. The leaderboard is mostly step five and step six, lol.</p>

The trial that is supposed to settle it</h2>
TRIUMPH-5 is the step-one version: retatrutide against tirzepatide, same people, same protocol. If it reads out roughly on schedule, a lot of the cross-trial arithmetic above becomes trivia. It will answer how much more weight loss the third receptor buys, in a population where both drugs ran under identical rules. It will also produce the comparison of tolerability that the network meta-analysis could only estimate from separate trials.</p>
It does not answer everything, for instance outcomes. Tirzepatide has cardiovascular data: SUMMIT showed a 38% reduction in cardiovascular death or worsening heart failure, and SURPASS-CVOT found it noninferior, but not superior, to dulaglutide. Retatrutide so far has things like a post hoc analysis of lipoprotein and inflammatory biomarkers from its phase 2 trials. Biomarkers are stuff that might predict outcomes. They are not outcomes, and that gap is not closed by a weight-loss trial, however clean.</p>
And I suppose there is the naming. A head-to-head trial carries real risk for whichever drug is supposed to win, and it must be hard to call your program TRIUMPH and then learn the answer in public. I’m sure that consideration never entered anyone’s planning at all.</p>
Until the data is out, the cleanest summary is the boring one: three receptors have beaten two in every comparison so far, and none of those comparisons was a fair fight.</p>

Tirzepatide: How One Molecule Hits Two Receptors

2026-11-01T00:00:00+00:00

The way a hormone drug usually works is that you take a hormone the body already makes, find the receptor it plugs into, and build a sturdier copy that plugs into the same receptor and lasts longer. The drug this article is about does something greedier: tirzepatide is, in the words of a review titled “The Cardiovascular Effect of Tirzepatide,” “a 39-amino-acid synthetic peptide functioning as a dual GIP/GLP-1 receptor agonist.” One molecule switches on two different receptors, the ones for the gut hormones GIP and GLP-1. (The same review reports that this earned it the nickname “twincretin,” which is a word somebody said out loud and then kept.)</p>

And it works. In the SURMOUNT-1 phase 3 trial in adults with obesity, the drug produced mean weight reductions of 19.5% at a 10mg dose and 20.9% at 15mg. Drugs that hit only the GLP-1 receptor land at approximately 6% to 15% weight loss in clinical trials, according to one pharmacology review, while dual GIP/GLP-1 agonists land at approximately 15% to 20%. So the second receptor seems to be adding something. What exactly it adds is the part the field has not worked out, and it is a stranger gap than it sounds.</p>

How one peptide fits two different receptors</h2>
Start with why this is possible at all. A structural paper on incretin receptors describes the GIP receptor and the GLP-1 receptor as “homologous GPCRs,” meaning they are related proteins from the same family, built on similar plans. A peptide hormone is a chain of amino acids, and the receptor reads parts of that chain. If two receptors read chains in broadly similar ways, a single chain can, with enough editing, read acceptably to both.</p>
Here is what the editing looks like, borrowed from a neighboring problem. Structural work on dual agonists of the GLP-1 and glucagon receptors (a different pair, but the same kind of puzzle) found that differences in the first three residues of the peptide determine which receptor it prefers, through how those residues engage a deep binding pocket. The middle of the peptide, meanwhile, recognizes two extracellular loops and the top of the first transmembrane helix. So a few amino acids at the front end do a lot of the choosing, and the rest of the chain does a lot of the holding on.</p>
The relevant legal standard, as I understand it, is not that the molecule fit each receptor perfectly. It is that the molecule fit each receptor to a degree the parties find commercially reasonable, said degree to be determined by the receptor in its sole discretion and reviewed by the regulator at the regulator’s leisure. In practice this means a lot of meetings where a medicinal chemist says something like (I am inventing this) “can we make residue two a little more GIP without making it a lot less GLP-1?” and everyone stares at a binding curve.</p>
The resulting relationship between one molecule and two receptors is, let’s say, blurry. It is committed to the GLP-1 receptor. It also sees the GIP receptor regularly. Everyone involved has agreed this is fine.</p>

What imbalanced agonism means</h2>
Once you have one molecule hitting two receptors, you have a ratio. The molecule activates receptor A by some amount and receptor B by some other amount, and because it is a single molecule, those amounts travel together. You cannot take a little extra GIP on Tuesdays (the molecule is not taking requests). The idea behind imbalanced agonism is that this ratio does not have to be one-to-one, and that the best version of a dual agonist might be deliberately lopsided toward one receptor.</p>
So the dial, for the people running a trial, is the dose. Actually, that is not quite right. The dose turns both receptors up at once, in a proportion that was welded into the molecule at the chemistry stage, so the only dial that really sets the balance is the one the chemists turned years before anyone enrolled a patient. By the time you are choosing between 10mg and 15mg, the argument about balance is over.</p>
This is in some sense the opposite of a combination product. CagriSema, for instance, is a fixed-dose combination of two separate molecules, semaglutide and the amylin analogue cagrilintide. Two molecules can in principle be rebalanced by changing how much of each goes in. One molecule cannot. A single-molecule dual agonist is a bit like a two-way player in baseball, the one who pitches and hits: very efficient, and you do not get to trade the pitching half.</p>
How lopsided tirzepatide actually is, and how much of its effect each receptor carries, is not settled by the sources I am working from, and I am not going to make up a ratio. (This is the kind of honest sentence that makes for a shorter article, a problem I have mostly solved by writing longer ones.) One broad review lists “biased agonist design” as one of “the three major axes of next-generation incretin drug development,” which tells you the field thinks the shape of the activation, and not just its existence, is where the next round of gains lives.</p>
To see why one molecule beats the alternative, consider a scenario I am making up. Suppose instead you sold GLP-1 and GIP as two separate injections and let the balance be tuned per patient. Then someone notices that the best ratio might drift with weight, so you add a third vial for adjustments. Then a fourth for weekends. Soon every clinic needs a pharmacist doubling as a bartender who mixes each patient’s weekly incretin cocktail to order, and the trials become impossible to run because no two arms got the same drink. One fixed molecule is less flexible and vastly easier to test, approve and make.</p>

What the SURMOUNT trials showed for tirzepatide</h2>
The headline is the SURMOUNT-1 result: 19.5% mean weight reduction at 10mg and 20.9% at 15mg, in adults with obesity. Across the phase 3 SURMOUNT program, the drug showed superior weight reduction compared with GLP-1 monotherapy, and a review of pediatric obesity treatment states the adult case flatly: tirzepatide has shown “greater weight-loss efficacy than selective GLP-1 receptor agonism in adults.”</p>
The comparison holds up when somebody pools the trials. A review in Annals of Internal Medicine looked at 12 GLP-1 receptor agonists and coagonists across 26 randomized controlled trials involving 15,491 adults without diabetes. Tirzepatide came in at 17.8% weight loss, ahead of subcutaneous semaglutide at 13.9%, and behind the triple agonist retatrutide at 24.2% on 12 mg weekly. (Whether that third receptor is worth it gets its own article on this site.)</p>
There is also SURMOUNT-MMO, a trial designed to test whether the drug reduces morbidity and mortality in adults with obesity. Its rationale and design have been published. Its results are not among what I can report here. Weight loss is the number everyone quotes. Hard outcomes are what eventually matter.</p>

Three ways to read the extra weight loss</h2>
There are, roughly, three ways to read the gap between a GLP-1-only drug and a GIP/GLP-1 dual.</p>
The first reading is the straightforward one: GIP does its own useful stuff, and stacking a second incretin signal on the first gets you more effect than either alone. This is the story the molecule was built to tell. It has some biology behind it; even rat pancreatic alpha-cells, for instance, carry functional receptors for both hormones, so the two signals plainly overlap in the body. Two signals, more effect. Tidy.</p>
The second reading is that the dual agonist is, mostly, an excellent GLP-1 drug, and the GIP arm is a cooperative passenger whose contribution is real but hard to isolate. I guess the trouble with this reading is also its appeal: a head-to-head trial against a GLP-1-only drug tells you the package works better, not which half of the package is doing the work. The comparison numbers above cannot separate those.</p>
The third reading is the uncomfortable one. Look, there is another drug in development, maridebart cafraglutide, a bispecific antibody that combines GLP-1 receptor activation with GIP receptor blockade. It pushes the GIP receptor in the opposite direction. And it also appears to add weight loss on top of GLP-1 agonism. A paper titled “The Premise of the Paradox” calls this “a central unresolved scientific question in incretin pharmacology,” which is a polite way of saying that switching the receptor on and switching it off both seem to help.</p>
It is not obvious how both can be true. I don’t know, and neither, as of the sources here, does anyone else with certainty. One possibility is that long-term activation and blockade converge on some similar downstream state. Another is that the GIP effect is smaller or stranger than either design assumed. I suppose a third is that the two programs are measuring different things and calling them the same thing. If you designed a molecule around the premise that GIP agonism is good, you would like this question resolved in your favor, and the answer is currently arriving from a competitor whose premise is that GIP antagonism is good.</p>
If you want to find out what your second receptor is really worth, you had better hope the people trying to switch it off keep running their trials.</p>

Triple Agonists: Why Three Receptors Might Beat Two

2026-11-01T00:00:00+00:00

Somebody took a drug that activates two hormone receptors, noticed it worked very well, and decided to build one that activates three, including one whose main day job is raising blood sugar. That is the triple agonist: a single engineered peptide that switches on the GLP-1 receptor, the GIP receptor and the glucagon receptor at the same time. Retatrutide is the famous one (it has its own pages on this site, several of them). A newer entrant, UBT251, is described in its phase 1a/1b study as “a novel triple agonist peptide targeting the GLP-1, GIP, and glucagon receptors.”</p>

Why might three beat two? GLP-1 and GIP mostly work on the eating side, glucagon works on the burning side, and the two incretins are supposed to cancel glucagon’s habit of pushing up blood sugar. No head-to-head trial in front of me settles whether three actually beats two. What exists is a cross-trial picture. A review in Annals of Internal Medicine covered 26 randomized trials and 15,491 adults without diabetes. It put retatrutide at 24.2% weight loss at 12 mg weekly, ahead of tirzepatide at 17.8% and injectable semaglutide at 13.9%. That is a respectable gap. It is not a proof.</p>

The sensible objection to a triple agonist</h2>
Let us establish terms with appropriate rigor. A drug that activates one receptor is a mono-agonist. A drug that activates two is a dual agonist. A drug that activates three is a triple agonist. The reader who has followed so far has demonstrated the ability to count to three, and should hold the ability to count to four in reserve, because it will matter later.</p>
Now the objection. This looks like razors. For years the razor companies kept adding blades (at some point the handle was mostly a delivery mechanism for blades), and eventually everyone understood that blade count was a marketing number more than a shaving number. Tirzepatide was already nicknamed the “twincretin” (the field rarely passes up a pun), a 39-amino-acid peptide hitting the GIP and GLP-1 receptors, and a pharmacodynamics review puts dual GIP/GLP-1 agonists like it at roughly 15 to 20% weight loss in trials. So is the third receptor just a third blade?</p>
To be fair, that is a reasonable suspicion about any pharmaceutical franchise. But the third receptor is not more of the same. It does something the other two don’t, it also does something you very much don’t want, and the whole design is an argument that the other two can cancel the bad part. That is weirder than a blade. It is like adding a blade that nicks you, plus two blades whose job includes applying the bandage.</p>

Why put a blood-sugar hormone in a metabolic drug</h2>
Glucagon tells the liver to release glucose. If you are designing a drug for a population full of type 2 diabetes, it is the last hormone you would invite. The case for inviting it anyway is energy expenditure. A review of next-generation multi-agonists says dual GLP-1/glucagon agonism “increases energy expenditure by stimulating fat oxidation and glucose production, distinguishing it from the appetite-focused GLP-1/GIP approach.” (Note that “glucose production” is listed as part of the mechanism, not as a side issue.)</p>
In plain words: the glucagon part turns up the furnace, and the GLP-1 and GIP parts follow it around mopping up the sugar the furnace spills. The furnace has an official name, adaptive thermogenesis, and researchers have proposed that these agonists drive it by changing amino acid metabolism and immune cells in brown and beige fat. The mopping is spelled out in a review of glucagon signaling, which describes mazdutide, survodutide and retatrutide as glucagon-based multi-agonists that “incorporate GLP-1 receptor-activating moieties to counteract glucagon’s hyperglycaemic effects.”</p>
Here is a made-up household version. You want to burn more fuel, so you run the heater all winter and the air conditioner at the same time, and the living room stays at 70 degrees. The thermostat looks normal. The fuel tank drains. Your neighbor, impressed, installs a second heater and a second air conditioner, and her house is also 70 degrees, and the utility company starts sending both of you holiday cards. The mechanism is not fully settled, either. One mouse study found that bile acid binding resins boosted glucagon-driven weight loss, which suggests bile acids are part of the furnace too.</p>

How one peptide gets three receptors to say yes</h2>
Getting a single molecule to hook up with three choosy receptors, on terms each one finds attractive, is the actual chemistry problem. Retatrutide’s development reportedly took advances in peptide design, amino acid modification and medicinal chemistry. You can imagine the meeting. “Hey, what if it also hits glucagon?” “Doesn’t that raise blood sugar?” “Sure, but we have two other receptors for that.”</p>
The best public window into the tuning comes from dual GLP-1/glucagon agonists. A study titled Structural analysis of the dual agonism at GLP-1R and GCGR used cryo-EM to image both receptors bound to three of them: peptide 15, cotadutide and SAR425899. The three had different activation profiles at each receptor. The middle of each peptide grips the receptor’s outer loops, and selectivity comes down to the very front: the study found “differences in side chain orientations within the first three residues” that point to “distinct engagements in the deep binding pocket.” (I write jokes about drug pipelines, so I will take their word on the deep binding pocket.)</p>
The point is that the first three amino acids help decide which receptor gets more of the action. A triple agonist is not three drugs taped together. It is one chain whose front end has to be acceptable to three locks, in proportions someone chose on purpose.</p>

What is actually in development</h2>
A network meta-analysis of 14 randomized trials of glucagon receptor agonists ranked the field by weight loss against placebo. Retatrutide came first at 13.44 kg, survodutide at 10.74 kg and mazdutide at 6.47 kg (the last two are glucagon-plus-GLP-1 duals, not triples). Retatrutide also had the largest HbA1c reduction and was the only one whose HbA1c effect reached statistical significance. On the other hand, the confidence intervals for retatrutide and survodutide overlap, which is the statistician’s way of saying slow down.</p>
UBT251 is the other triple with real data. In a phase 2 trial of 205 adults with obesity over 24 weeks, it produced weight loss of 13.6% to 19.7% depending on dose, against 2.0% on placebo. One headline on the results called it “Novo Nordisk’s triple agonist.” Nearly a fifth of body weight in under six months is, by most standards, a fair amount.</p>
The duals keep feeding the triple story. Cotadutide, a GLP-1/glucagon dual, has early data suggesting benefits on albuminuria and cardiorenal markers. Survodutide is aimed at the liver, and has its own article, etc. Anyway, the triple is mostly a bet that glucagon’s extras survive having GIP added on top.</p>

Where counting receptors stops being simple</h2>
Here is where the reserved skill comes in. Amycretin, Novo’s single-molecule GLP-1 and amylin drug, is described in one outlet as an agonist of GLP-1, amylin and calcitonin receptors, which is three targets. Elsewhere it is a two-hormone molecule. Whether it is a triple agonist depends on who is counting, and on whether calcitonin gets its own line in the slide deck or whatever.</p>
The stranger problem is GIP. Tirzepatide activates the GIP receptor. Amgen’s maridebart cafraglutide, a bispecific antibody, blocks it while activating GLP-1. Both add weight loss on top of GLP-1. A review called The Premise of the Paradox describes this as “a central unresolved scientific question in incretin pharmacology.” The triple agonist’s logic assumes each receptor you switch on contributes something. For GIP, switching it off also contributes something.</p>
Which means the logical next molecule turns the GIP receptor on and off at the same time, and the slide deck counts it as four.</p>

The Wegovy Pill: How Oral Semaglutide Works

2026-11-01T00:00:00+00:00

Novo Nordisk sells a drug called semaglutide as a once-weekly injection named Wegovy, at a dose of 2.4 milligrams. It has also run phase 3 obesity trials of a version you swallow, and that version used a dose of 50 milligrams. Same molecule. Roughly twenty times the amount.</p>

So here is the plain answer for anyone who searched it: the Wegovy pill is oral semaglutide, the same GLP-1 peptide that is in the injection, formulated with an absorption enhancer called SNAC so that some of it makes it from the stomach into the blood. Most of it does not make it, which is why the dose is so much bigger than the shot’s. A 2026 systematic review put its placebo-subtracted weight loss in adults without diabetes at 14.3%. Whether and when it is approved for weight loss in any particular place is something the sources I am working from do not settle, so I will not pretend they do.</p>

Why you can’t just put the injection in a pill</h2>
Start with the small, reasonable version of the problem. Semaglutide is a peptide, which is a short chain of amino acids, which is to say it is a small piece of protein. The human digestive tract is, professionally, a machine for taking protein apart (this is the whole point of lunch). If you swallow a peptide drug, your stomach does not know it is medicine. It treats it like a bite of chicken.</p>
An injection skips all that. You put the molecule under the skin, it goes into the blood, and it does its job, which for semaglutide is mimicking the gut hormone GLP-1 (the site has a whole article on what an incretin is, so I will leave that there). Wegovy got its weight-loss approval in 2021 as a weekly shot. In the STEP-1 trial, which enrolled 1,961 adults with obesity or overweight, people on semaglutide 2.4 mg lost 14.9% of their body weight on average, versus 2.4% on placebo, and 69.1% of them lost at least 10%.</p>
That is a good drug. On the other hand, it is a needle. Everyone involved here is acting sensibly from where they stand: lots of people would rather swallow something than inject it, Novo would like to sell its molecule to those people too, and regulators would like to see that the swallowed version actually does what the injected one does. That’s fine. It just means somebody has to get a protein through a stomach.</p>

How much semaglutide you have to swallow, escalating</h2>
Here is a hypothetical, and I am making it up as I go. You are a formulation chemist. Your boss hands you the 2.4 mg weekly dose and says “put this in a tablet.” You do. Almost none of it reaches the blood, because the stomach digests it and the gut lining is not in the habit of letting big molecules wander through.</p>
So you add more semaglutide. Some fraction survives. Then you add a helper molecule whose job is to get the peptide across the gut wall, and a bit more survives. Then you notice that the amount surviving is still tiny, so you add more peptide again. At the weekly meeting someone says “okay, but what if we just make the whole tablet bigger,” and nobody has a better idea, so you do that.</p>
Now push it. Keep going and you end up with a drug that is absorbed so badly that patients eat it by the bowl. A breakfast cereal of semaglutide, sold in the Costco-size box, where each flake is mostly helper molecule and a little bit of medicine, and the pharmacist says “your prescription is out back by the loading dock.” The manufacturing plant has to produce a mountain of peptide so that a thimble of it shows up in anyone’s bloodstream. The economics are weird. The chemistry is merely sad.</p>
How far along that road is the real world? Somewhat far. The injection is 2.4 milligrams. The oral dose in the phase 3 obesity work was 50 milligrams.</p>

Dwelling on the number 50</h2>
I would like to spend a moment with 50, because it is a marvelous number in this context. Fifty divided by 2.4 is 20.83. So each oral dose contains about twenty-one injections’ worth of semaglutide. (My job, it turns out, consists largely of dividing one number by another and then acting surprised.)</p>
And that is per dose. The injection is weekly. If a pill were taken every day (the sources I have do not spell out the schedule, so treat this strictly as arithmetic on a hypothetical), the weekly total would be 350 milligrams against the shot’s 2.4, which is about 146 times as much molecule to land in roughly the same place. The point is that almost all of what you swallow is, in the end, chicken.</p>
This is the core answer to why the oral dose is so much larger. It is not that the pill is a stronger drug. It is the same drug, delivered through a route that throws most of it away, so you have to start with a lot more to finish with enough.</p>

How SNAC gets the Wegovy pill past the stomach</h2>
The helper molecule in the real product is SNAC, the absorption enhancer. The general idea of an absorption enhancer is to make the local environment friendlier for long enough that a large molecule can get across the gut lining, rather than being broken up first. SNAC’s role is basically that of an escort: it accompanies the peptide on a short trip it could not manage alone and makes sure it gets where it is going.</p>
The detailed chemistry of how SNAC does this is not in the sources I am working from, so I am not going to invent it. What the sources do establish is the result: enough semaglutide gets through, at 50 mg, to produce weight loss in the same territory as the shot. It is a little like the heist in Ocean’s Eleven, if most of the crew got caught at the door and the plan was simply to bring a much larger crew.</p>

What the OASIS trials and the reviews showed</h2>
The phase 3 program for oral semaglutide in obesity (the OASIS trials) was early to the finish line. A 2024 paper, “Emerging pharmacotherapies for obesity: A systematic review,” put it this way: “Oral semaglutide 50 mg was the only emerging antiobesity medication to have completed a phase 3 trial as of the 2024 systematic review.” Everything else in the oral obesity pipeline was, at that point, still on the way.</p>
The efficacy number is the 2026 systematic review’s: placebo-subtracted weight loss of 14.3% for oral semaglutide in adults without diabetes, with a 95% confidence interval of 17.2% to 11.4%. For comparison, a review in Annals of Internal Medicine covering 26 trials and 15,491 adults without diabetes put subcutaneous semaglutide at 13.9%. I feel like the obvious reaction is that the pill seems to do at least as well as the shot, which is weird for a drug that loses most of itself on the way in. But these are different analyses pooling different trials, and the honest reading is that the two land in the same range, not that swallowing is better.</p>
There is also cardiovascular data. The SOUL trial, according to a review titled “GLP-1-based therapies in cardiovascular disease,” “reported a 14% reduction in MACE with oral semaglutide,” MACE being major adverse cardiovascular events, meaning heart attacks, strokes, cardiovascular deaths and so on. The weight-loss drugs keep turning out to be heart drugs, etc.</p>

Where the pill sits in the pipeline</h2>
One review of GLP-1 biology says that dual and triple agonists, biased agonist design, and oral formulations are “the three major axes of next-generation incretin drug development.” Translated: drug companies are trying to make these molecules hit more receptors, hit them more cleverly, or come in a pill. Oral semaglutide is the third axis done the brute-force way.</p>
The other way is a small molecule that is not a peptide at all and so does not get digested, which is what Eli Lilly’s orforglipron is (it has its own article here). Anyway, Novo has not abandoned the brute-force approach. Its oral amycretin, a single molecule hitting GLP-1 and amylin receptors, produced 13.1% weight loss versus 1.2% on placebo after 12 weeks in a phase 1 trial, at 100 mg per day, and a phase 3 oral trial called AMAZE 9 began recruiting in August 2026. Big peptide, big dose, big tablet, or whatever. If you want people to swallow your peptide, you had better make a great deal more of it.</p>

When Will Retatrutide Be Available? The Regulatory Path

2026-11-01T00:00:00+00:00

Today the most effective weight-loss drug anyone has tested in a big trial is not for sale anywhere, and its maker does not plan to ask the US government for permission to sell it until next year. The drug is retatrutide, from Eli Lilly. The Remy Research pipeline report describes its status about as plainly as a status can be described: it “is not approved in any country.”</p>

So, when will retatrutide be available? Not before 2027, and probably not until well after the start of it. Lilly plans to submit retatrutide for US regulatory approval in Q1 2027. A normal FDA review runs 10 to 12 months. Add those together and you get a plausible approval around early 2028, assuming the review goes smoothly and nothing speeds it up or slows it down. The available facts settle neither of those things.</p>

Why the answer to when retatrutide will be available is a filing date</h2>
The way to think about this is to follow who gets paid for what. Lilly gets paid when it sells a drug. It can sell a drug in the US only after the FDA approves it. The FDA approves a drug when it receives a filing showing the drug works and is safe enough. The filing is built out of Phase 3 trials. Phase 3 trials take years.</p>
Every link in that chain is reasonable. Each one exists because, at some point, someone sold something that did not work, or worked and also did something else. The chain is slow on purpose. Slowness is the product.</p>
The chain also ends somewhere nobody designed. We’ll get there. It involves vials.</p>

What the Phase 3 readouts actually showed</h2>
The first Phase 3 result was TRANSCEND-T2D-1, a trial in adults with type 2 diabetes whose blood sugar was not controlled by diet and exercise alone. It ran 40 weeks with 537 participants. HbA1c (a measure of average blood sugar) fell by 1.69, 1.86 and 1.94 percentage points at the 4 mg, 9 mg and 12 mg doses, against 0.81 for placebo. Weight fell 11.5%, 13.9% and 15.3%, against 2.6% for placebo.</p>
The big one was TRIUMPH-1, an 80-week obesity trial that reported its topline on May 21, 2026. On the 12 mg dose, people lost 28.3% of their body weight. Well, more precisely: they lost 28.3% by the “efficacy estimand” (n=2,339), and “up to 25%” by the “treatment-regimen estimand,” which are two different statistical answers to the question of what happened in the same trial. Roughly, one asks what the drug does when people stay on it as planned, and the other counts everyone who was assigned to it. Drug companies report both (it would be rude to waste a perfectly good estimand). The bigger number gets the headline.</p>
Either way it is a lot. The 12 mg group started at an average body weight of 248.5 lb and lost an average of 70.3 lb. Of those participants, 45.3% lost 30% or more of their body weight, and 65.3% got their BMI below 30. In a blinded extension for people who started with a BMI of 35 or higher, the 12 mg group reached 30.3% weight loss by week 104. AJMC summarized it this way: “All three doses of retatrutide (4 mg, 9 mg, 12 mg) met the primary and key secondary endpoints in TRIUMPH-1.”</p>
There is also TRIUMPH-2, a Phase 3 trial in adults with both obesity and type 2 diabetes. Its results are not in the material I’m working from, so I won’t pretend to know them. They will presumably show up in the filing. (The site’s other retatrutide articles go through the numbers more carefully than this one has room to.)</p>

Why Lilly files in 2027 instead of now</h2>
Here is the puzzle. The headline obesity data came out in May 2026. The filing is planned for Q1 2027. Why the gap?</p>
The facts do not say. Presumably the answer is boring. A topline is a press release (a genre whose main virtue is fitting on one screen). A filing is a regulatory dossier that has to contain everything, from full datasets for every trial to safety tables and manufacturing details. I assume Lilly also wants more of its Phase 3 program finished, so the label covers more uses. (I write about drug trials for a living, which mostly means reading the word “estimand” more times per week than any normal person reads it in a lifetime, and even I would not want to assemble one of these.)</p>
It’s fine. The incentive actually points the same way as the patience. A drug that gets approved for a narrow use and then has to come back for a broader one has spent years selling less than it could have. A drug that files once, with everything, launches big. I’d rather not think too hard about what Lilly’s launch planners have penciled in for its competitors.</p>
You can picture the conversation at the agency, which I am inventing: “Hey, thanks for the 80-week topline, love the chart, can we see the actual data now?”</p>

How long the FDA takes once it has the file</h2>
The normal FDA review takes 10 to 12 months. There is a newer program, the Commissioner’s National Priority Voucher, which according to BioSpace “sought to shorten FDA regulatory review timelines” to 1 to 2 months. That would turn a year into a few weeks, which is sort of the regulatory equivalent of an airport fast lane that skips security, check-in and also most of the airport.</p>
But look, the same BioSpace report was about the FDA delaying decisions for Lilly’s obesity pill orforglipron and other voucher holders. So the fast lane has, at least once, been slower than the sign promised. Whether retatrutide gets a voucher at all is not in the facts. I don’t know, and none of the reports I’m working from say.</p>
So here is the arithmetic, between us. Filing in Q1 2027. Add a normal review. Approval, if it comes, lands somewhere around early 2028. Add a voucher that works as advertised and it could be spring 2027. Add a voucher that works the way the orforglipron one did and nobody can tell you. That is a range, not a date, and it is the honest one. Then there is the time to manufacture, ship and get the drug covered, which is its own chain I won’t follow here.</p>

Why research peptide sellers are not the answer</h2>
Now the end of the chain. Lilly makes money only after approval. The FDA approves only after the trials and the review. So for several years there is a drug with a 28.3% headline and no legal way to get it outside a trial. Demand does not wait for the review clock.</p>
So websites sell vials labeled “retatrutide,” marked for research use. I mean, consider what that label is actually doing. The thing the trials tested is a specific molecule, made a specific way. An explainer titled What Is Retatrutide? calls it “an engineered amino-acid sequence rather than a naturally occurring human peptide,” and notes it had to stay active at three different receptors while keeping its stability, receptor affinity and pharmacokinetics all at once. That is hard chemistry. Whether a given vial contains that molecule, at that purity, in that amount, is exactly what the regulatory path exists to check. For these vials, nobody has checked.</p>
Here is a made-up scenario, to be clear invented. A seller lists “retatrutide, for research only.” Customers ask for dosing guidance. The seller cannot give it without admitting the research is happening in people, so the listing adds “not for human use.” Sales rise. The seller adds a lab coat to the product photo. Sales rise again. Eventually the vial has more disclaimers than peptide, and the most carefully tested thing in the box is the font.</p>
None of this makes the drug available. Availability, in the sense the search phrase means, is an approval and a pharmacy and a label. Everything before that is just the chain running. In the beginning, before anyone outside a lab had heard of it, retatrutide was known only by its research identifier, LY3437943.</p>