Retatrutide: the triple agonist, what the research shows now, and the horizon

A synthetic peptide that does, in one molecule, what three hormones do apart: phase 2, the published TRIUMPH phase 3 studies, and the horizon as an outlook.

Peptalis: for laboratory research use only. Not for human use.

A synthetic peptide that does, in one molecule, what three hormones do apart, and an example of how to weigh a strong signal honestly.

The first crash course named metabolic regulation as one of the six research areas where peptides draw attention. Few molecules illustrate that area as sharply as retatrutide.

Retatrutide is a synthetic peptide that does, in a single molecule, what three separate hormones normally do apart. That makes it scientifically interesting, and a useful example of how to weigh a strong signal honestly, even when it is large.

The setup is deliberately twofold. First the foundation: what retatrutide is, how it works, and what the clinical research shows now. Then the horizon: what that could mean for the future, explicitly as an outlook.

That separation is not a stylistic choice. The first large phase 3 studies of retatrutide have been completed and were published in 2026 in The New England Journal of Medicine and The Lancet, and the manufacturer has announced it is preparing a regulatory application. Keeping the line between what has been shown and what still has to be confirmed is the point of this piece.

Fig. 0The piece falls in two halves: left solid and filled (demonstrated), right lighter and dashed (outlook). The division itself is the message.

Part A · The foundation

What retatrutide is, how it works, and what the clinical research shows now.

Part 1

What retatrutide is

Objective: After this part it is clear what kind of molecule retatrutide is, and which research phase it is in.

Fig. 1Schematic: a chain of 39 amino acids with one fatty-acid side chain that couples to albumin. That coupling is why once-weekly dosing is possible in research.

Retatrutide, referred to in the early literature as LY3437943, is a synthetic peptide. It is built from thirty-nine amino acids and was developed by Eli Lilly.

Its sequence draws on an endogenous hormone but is modified at several points. It contains non-natural amino acids that make the molecule more stable, and it carries a fatty-acid chain.

That fatty-acid chain has a practical function. It lets the peptide bind reversibly to albumin, a transport protein in the blood, so the molecule lasts longer and can be given under the skin once a week.

One point belongs here immediately, and it shapes how the rest should be read. Retatrutide is a medicine under clinical investigation. As of this piece's reference date it is not an approved drug, although the manufacturer has announced it intends to seek approval (see part 6). What follows describes what studies did and measured, not what the molecule should do in any individual.

Takeaway. Retatrutide is a synthetic 39-amino-acid peptide with a fatty-acid chain for weekly dosing. It is an investigational medicine, not yet approved as of the reference date.

Part 2

Three receptors in one molecule

Objective: After this part it is clear why retatrutide is called a “triple agonist,” and what each of the three targets means in the research.

Fig. 2One molecule engages three receptors in research. The glucagon route (accented) is the distinguishing, new part. The labels describe routes under study, not effects in humans.

The crash course introduced peptides as messengers that fit onto receptors. Retatrutide is designed to fit onto three different receptors at once. Hence the name triple agonist, or triagonist.

Those three are the receptors for GIP, GLP-1 and glucagon: three hormones the body uses to regulate metabolism and blood sugar. An agonist is a molecule that activates a receptor, the way the body's own hormone would.

Two of these routes are familiar from earlier medicines. GLP-1 agonists and the combined GIP/GLP-1 agonist tirzepatide are already approved drugs; retatrutide adds a third route on top.

That third route is the distinguishing part. In research, the glucagon receptor is linked to energy expenditure and to the release of fat from the liver, a different angle from the appetite route that GLP-1 mainly engages.

The same caution applies here as always. That a molecule activates three receptors is a design feature, not proof that the combination works out better. Whether adding those three axes actually contributes anything is precisely what the research has to establish.

Takeaway. Retatrutide activates three receptors at once: GIP, GLP-1 and glucagon. The glucagon arm, linked to energy expenditure and liver fat, is what sets it apart from earlier medicines.

Part 3

Why this is an interesting research question

Objective: After this part it is clear why one molecule with three targets makes for an attractive, testable hypothesis.

Fig. 3The research question, not a ranking: does the third route add anything over one or two? The modules stand deliberately equal, with no ascending “gain”.

Part 2 leads to a logical question. If three hormone routes each drive a part of metabolism, does combining them in one molecule produce a stronger or broader effect than engaging a single route?

That is a hypothesis, not a conclusion. The appeal lies in the precision: a single defined peptide, with a known sequence, that deliberately engages three receptors and can therefore be compared against medicines that engage one or two.

That is exactly why this is an active research area. It makes the contribution of each individual route testable, and it places retatrutide in a direct comparison with existing, approved medicines.

What follows is how far that research has actually come. An attractive hypothesis says nothing yet about the strength of the evidence, and that distinction is what the next part is about.

Takeaway. The central question is whether three routes in one molecule deliver more than one. That is a testable hypothesis, and something other than a demonstrated outcome.

Part 4

What the research shows now

Objective: After this part it is clear which clinical studies of retatrutide have been done, what they measured, and at what level the evidence stands.

Fig. 4The phase 2 signals, confirmed in phase 3 in large groups and published in 2026. The phase 3 figures are the main analysis, which counts every participant. Study name and study size sit as prominently as the number: these are study results, not a promise.

The research now has two layers. First the phase 2 studies, which established dose, safety and early effects. Then the phase 3 programme, whose first large studies were published in journals in 2026. Below are the most important ones, each stated as a fact about that study.

The phase 2 studies: dose-finding.

Obesity. In a 48-week, double-blind, placebo-controlled trial in 338 adults with obesity or overweight (Jastreboff et al., New England Journal of Medicine, 2023), participants' body weight fell by a mean of 24.2% in the highest-dose group (12 mg weekly), against 2.1% on placebo.

Type 2 diabetes. In a trial in 281 people with type 2 diabetes (Rosenstock et al., The Lancet, 2023), HbA1c (a measure of average blood sugar) fell by 2.02 percentage points at 24 weeks in the 12 mg group, against almost no change on placebo. Body weight in that group fell by 16.94% at 36 weeks.

Liver fat. In a substudy in 98 participants with metabolic dysfunction-associated steatotic liver disease (Sanyal et al., Nature Medicine, 2024), liver fat fell by 82.4% at 24 weeks in the 12 mg group, against a slight rise on placebo. In 86% of participants in that group liver fat was below 5%, the threshold considered normal, against none on placebo.

The phase 3 programme: the first studies published.

Obesity without diabetes (TRIUMPH-1). The largest published study ran for 80 weeks in 2,339 adults with obesity or overweight without diabetes, who received 4, 9 or 12 mg of retatrutide or placebo once a week (Jastreboff et al., New England Journal of Medicine, 2026). In the main analysis, which counts every participant, including those who stopped along the way, body weight fell by a mean of 17.6%, 23.7% and 25.0%, against 3.9% on placebo.

The same study had two substudies. In the 574 participants with knee osteoarthritis, the pain score (WOMAC, on a scale up to 10) fell by 3.4 to 4.1 points, against 2.5 on placebo. In the 243 participants with obstructive sleep apnoea, the number of breathing pauses and shallow-breathing episodes per hour of sleep fell by 22.8 to 34.3, against 9.6 on placebo.

Why you also read 28%. For the same study the manufacturer reported a higher figure: 28.3% at 12 mg (Eli Lilly, 21 May 2026). That is a different way of counting, which estimates what the effect would be if every participant had kept using the medicine. Both figures belong to the same study. The 25.0% counts everyone and is the main analysis of the publication; the 28.3% is an estimate for the case in which everyone continues. In an extension to 104 weeks, in 532 participants with a BMI of 35 or higher who had kept using the medicine until then, the manufacturer reported a reduction of 30.3% in the group that had started on 12 mg.

Type 2 diabetes (TRIUMPH-2 and TRANSCEND-T2D-1). TRIUMPH-2 followed 1,152 adults with type 2 diabetes and obesity or overweight for 80 weeks (Bellido et al., The Lancet, 2026). Body weight fell by 11.9%, 16.8% and 18.8% at 4, 9 and 12 mg, against 5.1% on placebo. In TRANSCEND-T2D-1, 537 people with type 2 diabetes received retatrutide as their only medicine for 40 weeks (Bajaj et al., The Lancet, 2026). HbA1c fell by 1.69 to 1.94 percentage points, against 0.81 on placebo; body weight by 11.5% to 15.3%, against 2.6%.

Not yet published: TRIUMPH-3 and TRIUMPH-4. For two studies only manufacturer announcements exist. TRIUMPH-3 (1,949 participants with severe obesity and established cardiovascular disease; Eli Lilly, 23 July 2026) reported weight loss of up to 22.6% at 80 weeks, against 3.2% on placebo, using the way of counting that assumes continued use. Serious cardiovascular events occurred less often than expected in both groups. Depending on which events are counted, there were 44 with retatrutide against 52 with placebo, or 27 against 23; that is too few to draw a conclusion from. TRIUMPH-4 (445 participants with obesity or overweight and knee osteoarthritis; Eli Lilly, 11 December 2025) reported weight loss of 23.7% at 12 mg when every participant is counted (28.7% with continued use), against 4.6% on placebo, and a reduction in knee pain.

The effects come with the risk profile observed in these studies. Across phase 2 and phase 3, the most reported observations were gastrointestinal (nausea, diarrhoea, constipation, vomiting), dose-dependent and mostly mild to moderate. The phase 3 studies also reported dysaesthesia, an altered or unpleasant sensation in the skin: in TRIUMPH-2 in 7% of participants on 12 mg, against 1% on placebo, and according to the manufacturer in TRIUMPH-1 in 12.5%, against 0.9%. In TRIUMPH-2 low blood pressure was also more frequent: 6% on 12 mg, against less than 1% on placebo. The share of participants who stopped the medicine because of complaints ranged, in the phase 3 studies, from a few per cent to about eighteen per cent at the highest dose, against five per cent at most on placebo. The earlier phase 2 study had also seen a dose-dependent rise in heart rate, peaking around week 24 and declining afterwards.

Takeaway. The phase 2 studies showed large effects on weight, blood sugar and liver fat. The first phase 3 studies were published in 2026 and confirm this in thousands of participants: in the largest published study, body weight at the highest dose fell by a mean of 25.0% at 80 weeks, against 3.9% on placebo. Two phase 3 studies have so far only been reported by the manufacturer, and the long-term outcomes study is still running.

Part 5

Reading the evidence honestly

Objective: After this part it is clear how to weigh the state of the evidence on retatrutide honestly.

Fig. 5The same ladder as in the crash course and the database dot-meter. The position: the first phase 3 studies have been published peer-reviewed. A strong result, but the long-term outcomes are still open (dashed).

The previous parts showed strong figures, now across two phases. Two things hold at once, and neither should crowd out the other.

The first: the large effects from phase 2 held up in phase 3, and that is now in peer-reviewed publications. A mean weight reduction of a quarter of body weight was measured at the highest dose in a study with more than two thousand participants, over 80 weeks. That is no longer a single early signal. It is a consistent picture in large, controlled groups.

The second: three caveats remain. Not all phase 3 studies have been published; for TRIUMPH-3 and TRIUMPH-4 only manufacturer announcements exist. In the phase 3 studies dysaesthesia was more frequent than on placebo, in one study low blood pressure as well, and at the highest dose a share of participants stopped the medicine. And the question that weighs most in the long run, whether the weight loss translates into fewer cardiovascular, vascular and kidney events, is being tested in a separate outcomes study that runs for years and has no results yet.

That retatrutide is not yet approved as of the reference date fits this picture: the results are strong, the formal review has yet to begin. A large effect that holds up in phase 3 is a strong result, and at the same time not the last word on long-term safety and outcomes.

Takeaway. The phase 2 signals were confirmed in phase 3, and the first studies have been published peer-reviewed. What is still missing is the remaining publications, the direct comparisons with existing medicines and the long-term outcomes for the heart, blood vessels and kidneys. Both facts belong side by side.

Part B · The horizon

What this research could mean for the future, explicitly as an outlook.

Part 6

What the future could bring

Objective: After this part it is clear what perspective the research on retatrutide offers, explicitly as an outlook and not a promise.

This part is an outlook. It describes what the announced steps and ongoing studies have to establish, and what the triple-agonist approach could mean as a research direction. Nothing below is a commitment about an outcome or an approval.

Fig. 6The horizon. Left, the point reached; everything to its right is dashed: outlook, still to be shown. The regulatory submission is an announced step, not an approval.

The coming years will be decisive for this molecule, and that can now be stated concretely. In July 2026 the manufacturer announced it intends to submit a regulatory application (a Biologics License Application) to the US FDA in the first quarter of 2027. That would start a formal review; whether and when a regulator reaches approval is for that regulator to decide.

Two tracks reach beyond the scale. A large outcomes-driven study (ClinicalTrials.gov, NCT06383390) follows around 10,000 participants to test whether the effect translates into fewer cardiovascular, vascular and kidney events: the evidence that the weight studies by definition cannot deliver. Alongside it, direct comparisons with existing medicines are running, including a study against tirzepatide, which have to show what the third receptor route adds in practice.

Beyond this one molecule, a broader research direction is taking shape. Retatrutide is part of a larger idea: that combining several hormone routes in one peptide may deliver more than engaging a single one. Alongside retatrutide, other multi-agonists are being studied, and the question of which combination of routes adds most for which outcome remains wide open.

And that, honestly, is what makes this research area worth the effort. Not the certainty of an outcome, but a set of sharp, testable questions, with large studies and an approaching review now actually gathering the answers.

Scientific references

All references are PubMed-indexed and verified (as of October 2026). According to PubMed.

  1. 01Jastreboff AM, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. New England Journal of Medicine, 2023. Phase 2 RCT PMID 37366315 · DOI
  2. 02Rosenstock J, et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a phase 2 trial. The Lancet, 2023. Phase 2 RCT PMID 37385280 · DOI
  3. 03Sanyal AJ, et al. Triple hormone receptor agonist retatrutide for MASLD: a randomized phase 2a trial. Nature Medicine, 2024. Phase 2a RCT PMID 38858523 · DOI
  4. 04Jastreboff AM, et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. New England Journal of Medicine, 2026. Phase 3 RCT · TRIUMPH-1 PMID 42814954 · DOI
  5. 05Bellido V, et al. Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a double-blind, parallel-group, randomised, placebo-controlled, phase 3 trial. The Lancet, 2026. Phase 3 RCT PMID 42810372 · DOI
  6. 06Bajaj HS, et al. Efficacy and safety of retatrutide, a GIP, GLP-1, and glucagon receptor agonist, in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1): a double-blind, randomised, phase 3 trial. The Lancet, 2026. Phase 3 RCT PMID 42250575 · DOI
  7. 07Urva S, et al. The novel GIP, GLP-1 and glucagon receptor agonist retatrutide delays gastric emptying. Diabetes, Obesity and Metabolism, 2023. Mechanism · human PMID 37311727 · DOI
  8. 08Giblin K, et al. Retatrutide TRIUMPH registrational trials — rationale and design. Diabetes, Obesity and Metabolism, 2025. Trial design PMID 41090431 · DOI
  9. 09Drucker DJ. Efficacy and Safety of GLP-1 Medicines for Type 2 Diabetes and Obesity. Diabetes Care, 2024. Review PMID 38843460 · DOI

Phase 3 · manufacturer announcements (not yet peer-reviewed)

These figures come from Eli Lilly press releases; the studies are registered on ClinicalTrials.gov. Unless stated otherwise, they follow the manufacturer's way of counting (the effect with continued use). They have not been checked here against a peer-reviewed publication.

  1. 10TRIUMPH-1, additional figures: with continued use: weight −28.3% (12 mg, 80 wk), against −2.2% on placebo; extension to 104 wk at BMI ≥35 (n=532, all groups together): −30.3% in the group that started on 12 mg. Eli Lilly, 21 May 2026. NCT05929066
  2. 11TRIUMPH-3: severe obesity with established cardiovascular disease, n=1,949, 80 wk; weight −22.6% (12 mg), against −3.2% on placebo (with continued use); serious cardiovascular events, broad count: 44 against 52, hazard ratio 0.82 (95% confidence interval 0.55 to 1.22); narrow count (cardiovascular death, heart attack, stroke): 27 against 23, hazard ratio 1.12 (0.64 to 1.96); no demonstrated difference. Eli Lilly, 23 July 2026. NCT05882045
  3. 12TRIUMPH-4: obesity/overweight with knee osteoarthritis, n=445, 68 wk; weight −23.7% (12 mg, all participants), against −4.6% on placebo; with continued use −28.7%, against −2.1%; knee pain (WOMAC, all participants) −62.6%, against −35.1% on placebo. Eli Lilly, 11 December 2025. NCT05931367

Regulatory: Eli Lilly has announced it intends to submit a Biologics License Application (BLA) for retatrutide to the US FDA in the first quarter of 2027 (as of October 2026). Ongoing: the cardiovascular/renal outcomes study NCT06383390 (≈ 10,000 participants) and a direct comparison with tirzepatide, NCT06662383 (≈ 800 participants).

Read further

For how evidence levels are weighed per compound, the first crash course sets out the evidence ladder this piece rests on; the second explains why strong human evidence stays scarce for many peptides.

Peptides Crash Course →Why peptide research is scarce →Open the database →

Author: Michel van der Veen · Registered Nurse · Science Editor, Peptalis. Sources checked via PubMed · 9 references. This piece reports outcomes as facts about the relevant study or about the manufacturer/regulator and makes no claim about an effect in the individual reader. Retatrutide is an investigational medicine, not approved as of the reference date; the manufacturer has announced a regulatory application for the first quarter of 2027. Facts and references verified, as of October 2026.

Compounds in this article

For laboratory research use only. Not for human use.