Retatrutide: what the trials show, status and safety
Summary
Retatrutide is an experimental peptide that switches on three hormone systems at the same time. In a mid-stage trial, participants lost 24.2% of their body weight over 48 weeks. The later, larger trials report bigger losses, but so far only through press releases from the manufacturer. No medicines authority has approved it, and no completed trial shows that it prevents heart attacks or strokes.
Key findings at a glance
- 24.2% of body weight lost after 48 weeks. That was the highest dose in a mid-stage trial in 338 adults with obesity; people on a dummy injection lost 2.1% [1].
- 28.3% lost after 80 weeks in a late-stage trial. TRIUMPH-1 enrolled 2,339 adults, but the figure comes from a company press release rather than a scientific journal [2].
- Long-term blood sugar down by 2.02 percentage points after 24 weeks. A mid-stage trial in 281 adults with type 2 diabetes, against a drop of 0.01 points on placebo [3].
- Fat in the liver down by 82.4% after 24 weeks. A sub-study in 98 adults with fatty liver disease, while it rose slightly, by 0.3%, on placebo [4].
- No heart benefit shown. In TRIUMPH-3 the risk of a serious heart event was, if anything, slightly higher (hazard ratio 1.12), and the range compatible with the data, 0.64 to 1.96, was far too wide to conclude anything [5].
- Approved in no country. The manufacturer announced that it would apply for approval in the United States in early 2027, and by September 2026 it had not done so [6], [5].
- Banned in sport at all times. Category S0 of the 2026 prohibited list covers every substance that no health authority anywhere has approved [7].
What it is
Retatrutide is a peptide made in the laboratory, a chain of 39 amino acid building blocks. The drug company Eli Lilly developed it under the code LY3437943 [8], [9]. A single molecule switches on the docking points, or receptors, for three hormones at once: GIP, GLP-1 and glucagon. It has no brand name, because no product containing it has ever been approved.
A fatty acid chain of twenty carbons (a C20 fatty diacid) attached to the seventeenth building block (lysine 17) makes the peptide cling to albumin, a carrier protein in the blood [8], [10]. The body therefore clears it slowly, taking about six days to remove half a dose, which is why trials inject it once a week [11]. The nickname "reta" circulates online. It appears in no official register and carries no weight in any document.
Quick facts
| Field | Value | Ref |
|---|---|---|
| Development code | LY3437943, also written LY-3437943 | [8], [12] |
| Class | Triple GIP, GLP-1 and glucagon receptor agonist | [9] |
| Structure | 39 amino acids, C20 fatty diacid on lysine 17 | [8], [10] |
| Sequence | YAQGTFTSDYSILLDKKAQAAFIEYLLEGGPSSGAPPPS | [8] |
| Formula and mass, sodium salt | C221H342N46O68, 4,731 g/mol | [13] |
| Formula and mass, peptide backbone, estimated | C187H281N43O60, 4,091.5 Da | [8] |
| Half-life | About 6 days | [11] |
| Route in trials | Subcutaneous, once weekly | [11] |
| Status | Investigational, phase 3, approved nowhere | [6], [10] |
| Developer | Eli Lilly and Company | [9] |
| CAS registry number | 2381089-83-2 | [8] |
| UNII | NOP2Y096GV, free acid; LQ42M82ZU6, sodium salt | [8], [14] |
| PubChem CID | 171934787, sodium salt only; no record for the free acid | [13] |
| ChEMBL | CHEMBL5095485 | [15] |
| IUPHAR/BPS ligand | 13769 | [10] |
How it works
Retatrutide attaches to the docking points of three hormones that between them govern appetite, the release of insulin and how much energy the body burns [9].
- The GLP-1 docking point. Switching it on makes people eat less and slows the stomach down. A dedicated early-stage study confirmed that the stomach empties more slowly in people [16].
- The GIP docking point. Switching it on adds to the release of insulin and may strengthen the GLP-1 effect. In laboratory tests retatrutide is more active here than at the other two [9].
- The glucagon docking point. The idea is that this raises the amount of energy the body burns and changes how the liver handles fat [9]. That part has never been measured directly in people.
Blood sugar falls overall, even though glucagon on its own pushes it up. The published explanation is that the two gut hormone effects outweigh the glucagon effect [9]. What each of the three contributes in humans remains an assumption, because no trial was designed to tell them apart.
The third docking point is what sets retatrutide apart from its relatives. Semaglutide acts on GLP-1 alone, and tirzepatide on GIP and GLP-1.
What the trials found
Weight
Phase 2 RCT In this mid-stage trial, 338 adults with obesity were allocated at random to one of four doses or to a dummy injection. After 48 weeks their weight had fallen by 8.7%, 17.1%, 22.8% and 24.2% on 1, 4, 8 and 12 mg, against 2.1% on placebo. On the 12 mg dose, every single participant (100%) lost at least 5% of their body weight, 93% lost at least a tenth and 83% at least 15%, against 27%, 9% and 2% on placebo [1].
Mid-stage randomised trial in 338 adults with obesity, over 48 weeks. Source [1].
Phase 3 (press release only) TRIUMPH-1 followed 2,339 adults without diabetes for 80 weeks. The reported weight loss was 19.0%, 25.9% and 28.3% on 4, 9 and 12 mg, against 2.2% on placebo. Almost half of the 12 mg group, 45.3%, lost at least 30% of their body weight, against 0.5% on placebo [2].
Phase 3 (press release only) TRIUMPH-3 enrolled 1,949 adults who had severe obesity along with diagnosed heart disease. After 80 weeks the reported weight loss was 21.6% on 9 mg and 22.6% on 12 mg, against 3.2% on placebo [5]. TRIUMPH-4, in 445 adults with worn knee joints, reported 26.4% and 28.7% [17].
Blood sugar
Phase 2 RCT In 281 adults with type 2 diabetes, the long-term blood sugar value, which reflects the average of the past two to three months (glycated haemoglobin), fell after 24 weeks by 0.43 percentage points on the lowest dose of 0.5 mg and by 2.02 points on 12 mg. On placebo it barely moved, at 0.01 points, and in the group given the established drug dulaglutide it fell by 1.41 points. Every dose except the lowest beat placebo by a clear margin [3].
Phase 3 (press release only) TRIUMPH-2 followed 1,152 adults with type 2 diabetes. After 80 weeks the reported weight loss was 12.7%, 19.1% and 20.8% on 4, 9 and 12 mg, against 4.0% on placebo. Long-term blood sugar fell by 1.4 to 1.6 percentage points from a starting value of 7.7% [5].
Liver fat
Phase 2a RCT A sub-study planned in advance enrolled 98 participants who had no diabetes but whose livers consisted of at least 10% fat. Scans showed that after 24 weeks the fat content had dropped by 42.9%, 57.0%, 81.4% and 82.4% across the four doses, while it edged up by 0.3% on placebo. In the two highest dose groups, 79% and 86% of participants came back below the 5% mark that counts as a normal liver [4].
Knee pain
Phase 3 (press release only) In TRIUMPH-4, participants rated their knee pain on a standard questionnaire (the WOMAC score). Over 68 weeks the rating fell by 4.5 and 4.4 points from a starting level of 6.0, against 2.4 points on placebo. An analysis done after the fact found that 14.1% and 12.0% of treated participants were free of knee pain at week 68, against 4.2% on placebo [17]. No ranges of uncertainty and no full result tables were published.
Cardiovascular events
Phase 3 (press release only) TRIUMPH-3 had planned in advance to count serious heart events. Counted in the broader way, across five kinds of event, there were 44 on retatrutide against 52 on placebo, a risk 18% lower (hazard ratio 0.82), with a range of 0.55 to 1.22. Counted in the narrower way, across three kinds of event, there were 27 against 23, a risk 12% higher (hazard ratio 1.12), with a range of 0.64 to 1.96 [5]. Both ranges take in the possibility of no difference at all, so neither figure shows a benefit or a harm.
What is still unknown
- Whether it prevents anything. The trial built to answer that, TRIUMPH-Outcomes, enrols 10,000 people and will not reach its main result before February 2029 [18].
- Independent checking of the late-stage results. By 6 September 2026 not one late-stage trial had been published in full. The independently reviewed record stops at the mid-stage trials [19].
- How long the effect lasts. The longest anyone has been watched is 104 weeks, and only in an extension restricted to participants with a body mass index of at least 35 [2].
- How it compares. The trial that pits it directly against tirzepatide, TRIUMPH-5, has not reported [19].
- Interactions with other medicines. Because the stomach empties more slowly, anything swallowed alongside may be absorbed differently, and no study has looked into that [16].
Side effects and safety
Every safety figure below comes from trials run by the manufacturer. No authority has examined the substance, so there is no approved package insert, nobody has weighed the benefits against the risks, and nothing keeps track of side effects outside the trials.
Stomach and bowel problems dominate, and they become more common the higher the dose. These frequencies come from TRIUMPH-1, comparing the 12 mg dose with placebo [2]:
| Event | 12 mg | Placebo |
|---|---|---|
| Nausea | 42.4% | 14.8% |
| Diarrhoea | 32.0% | 13.5% |
| Constipation | 26.1% | 10.9% |
| Vomiting | 25.3% | 4.8% |
| Dysesthesia | 12.5% | 0.9% |
| Urinary tract infection | 8.4% | 5.3% |
Further findings across the programme:
- Odd skin sensations get more common at higher doses. Tingling, burning or numbness of the skin (dysesthesia) affected 8.8% of participants on 9 mg and 20.9% on 12 mg in TRIUMPH-4, against 0.7% on placebo. They were described as mostly mild [17].
- More people give up at higher doses. In TRIUMPH-1, 4.1%, 6.9% and 11.3% of participants stopped across the three doses, against 4.9% on placebo [2].
- The heart beats faster. In the mid-stage obesity trial the rise grew with the dose, peaked at week 24 and then eased off again [1]. An independent assessment puts the largest increase at 6.7 beats per minute and treats it as a possible harm [20].
- Irregular heartbeat has been flagged. A second independent review lists mild to moderate irregular heartbeat (arrhythmia) alongside the faster pulse, and calls for long trials that measure what actually happens to patients [21].
- The mid-stage trials saw no dangerous drops in blood sugar and no deaths. In the liver sub-study, 2 of the 98 participants had a serious adverse event, and there was no sign that the drug damaged the liver [3], [4].
One published case involves material obtained outside a trial. A 2026 report describes a man in his thirties with type 1 diabetes who injected himself with a product sold under this name and developed severe vomiting, a dangerous build-up of acids in the blood and sudden kidney damage [22]. The authors point out that nobody had verified what such a product contains, how pure it is or how accurately it is dosed.
The gaps matter as much as the figures. There is no independently checked long-term safety record, no full safety tables have been published for any late-stage trial, and the question of the faster pulse remains open.
Doses used in trials
The doses below are simply what the cited studies gave, listed so that the results can be understood. They are not advice on how to use anything.
| Study | Arms | Route | Duration | n | Ref |
|---|---|---|---|---|---|
| Phase 1b, type 2 diabetes (NCT04143802) | 0.5, 1.5, 3, 3/6 and 3/6/9/12 mg weekly | Subcutaneous | 12 weeks | 72 | [11] |
| Phase 2, obesity (NCT04881760) | 1, 4, 8 and 12 mg weekly, starting at 2 or 4 mg | Subcutaneous | 48 weeks | 338 | [1] |
| Phase 2, type 2 diabetes (NCT04867785) | 0.5, 4, 8 and 12 mg weekly; dulaglutide 1.5 mg comparator | Subcutaneous | 36 weeks | 281 | [3] |
| Phase 2a, liver fat substudy (NCT04881760) | 1, 4, 8 and 12 mg weekly | Subcutaneous | 24-week readout | 98 | [4] |
| TRIUMPH-1 (NCT05929066) | 4, 9 and 12 mg weekly, escalated from 2 mg every four weeks | Subcutaneous | 80 weeks plus 24-week extension | 2,339 | [2] |
| TRIUMPH-2 (NCT05929079) | 4, 9 and 12 mg weekly | Subcutaneous | 80 weeks | 1,152 | [5] |
| TRIUMPH-3 (NCT05882045) | 9 and 12 mg weekly | Subcutaneous | 80 weeks | 1,949 | [5] |
| TRIUMPH-4 (NCT05931367) | 9 and 12 mg weekly | Subcutaneous | 68 weeks | 445 | [17] |
The late-stage doses are public knowledge only because the manufacturer named them in its announcements [2], [5], [17]. The official trial registry itself lists them merely as dose 1, dose 2 and dose 3 [19].
Development and approval status
Programme timeline
- 2022Phase 1b results in type 2 diabetes publishedRef [11]
- 2023Both phase 2 trials published; the TRIUMPH phase 3 programme beginsNEJM and The Lancet, refs [1], [3], [19]
- 2024Phase 2a liver fat substudy publishedRef [4]
- 2025TRIUMPH-4 reports by press release in DecemberRef [17]
- 2026TRIUMPH-1 reports in May, TRIUMPH-2 and TRIUMPH-3 in JulyPress releases only, refs [2], [5]
- Q1 2027United States filing announcedAnnounced, not submitted as of 6 September 2026, refs [5], [23]
- 2029TRIUMPH-Outcomes primary completion, Februaryn = 10,000, ref [18]
- 2019 — the substance is given to people for the first time, in a single-dose study in 45 healthy adults [9].
- 2022 — the early-stage results in type 2 diabetes are published [11].
- 2023 — both mid-stage trials are published, and the late-stage TRIUMPH programme starts [1], [3], [19].
- 2024 — the liver fat sub-study is published [4].
- 2025 — TRIUMPH-4 reports its results by press release in December [17].
- 2026 — TRIUMPH-1 reports in May and TRIUMPH-2 and TRIUMPH-3 in July, and the manufacturer announces that it will apply for United States approval in early 2027 [2], [5], [23].
| Market | Status | Note | Ref |
|---|---|---|---|
| United States | Investigational | Filing announced, Q1 2027 | [6], [5] |
| European Union | Investigational | No authorisation | [24] |
| Germany | Investigational | Follows EU route | [24] |
| United Kingdom | Investigational | No authorisation | [25] |
| Australia | Investigational | No registration | [26] |
| Canada | Investigational | No identification number | [27] |
| Switzerland | Investigational | No authorisation | [28] |
Every official register behind this table was queried on 6 September 2026.
There is one way to obtain the drug before approval, and it is regularly mistaken for an approval. Since August 2026 an expanded access programme has been registered in the United States under the number NCT07629401 [29]. It is a compassionate route for a small number of individual cases, and no authority has weighed the benefits against the risks in order to open it [30].
Anti-doping
Retatrutide is banned in sport at all times, both in and out of competition. Category S0 of the 2026 prohibited list covers "any pharmacological substance which is not addressed by any of the subsequent sections of the List and with no current approval by any governmental regulatory health authority for human therapeutic use" [7]. In other words, the substance is not named on the list at all; it falls under the ban because no authority has approved it. Category S2 names no drugs of the GIP, GLP-1 or glucagon type. The wider picture for this class is at peptides banned in sport.
Compared with related peptides
| Peptide | Receptors | Status | Strongest weight result in its own trial | Half-life |
|---|---|---|---|---|
| Retatrutide | GIP, GLP-1, glucagon | Phase 3, approved nowhere | −24.2% at 48 weeks, phase 2, n = 338 [1] | ~6 days [11] |
| Tirzepatide | GIP, GLP-1 | Approved in many markets | −20.9% at 72 weeks, SURMOUNT-1, n = 2,539 [31] | ~5 days [32] |
| Semaglutide | GLP-1 | Approved in many markets | −14.9% at 68 weeks, STEP 1, n = 1,961 [33] | Not stated here |
| Survodutide | GLP-1, glucagon | Phase 3 | −14.9% at 46 weeks, phase 2, n = 387 [34] | Not stated here |
| Mazdutide | GLP-1, glucagon | Approved in China (2025), nowhere else | −14.0% at 48 weeks, GLORY-1, n = 610 [35] | Not stated here |
These five figures come from five different trials. The people enrolled, the length of treatment, the starting weights and the way the result was calculated all differ, so that column ranks trials rather than drugs. Retatrutide is also the only one of the five that no country has approved.
Five separate trials, not a direct comparison: the people enrolled, the length of treatment, the starting weights and the way the result was calculated all differ. Sources [1], [31], [33], [34], [35].
The programme contains only one direct comparison. TRIUMPH-5 puts retatrutide up against tirzepatide, and it has not reported [19]. Until it does, any claim that one is stronger than the other rests on arithmetic between separate trials rather than on evidence.
Common misconceptions
- "Retatrutide is just a stronger tirzepatide." They come from the same company and are injected the same way, but they act on different hormones and stand in completely different legal positions. Tirzepatide is approved in many countries; retatrutide is approved in none, and the trial comparing them has not reported [9], [19].
- "The late-stage results have been published." Every late-stage figure comes from a company press release. None has been checked by independent experts, and none comes with ranges of uncertainty or full result tables [2], [5], [17].
- "TRIUMPH-3 proves a heart benefit." That trial enrolled people who already had heart disease, which says who took part, not what the drug achieved. Its heart results point in both directions and prove neither [5].
- "Expanded access means you can get it." That programme is a compassionate route for individual cases that meet narrow criteria. It grants no approval and makes nothing generally available [29], [30].
- "Products sold under this name are the trial substance." A 2026 case report describes a severe metabolic crisis after someone used material bought online whose contents nobody had verified [22].
- "Reta is the drug name." The only names that count for anything are the official international name and the development code [8], [12].
Frequently asked questions
Is retatrutide approved anywhere?
No. The drug registers of the United States, Canada, the European Union, the United Kingdom, Australia and Switzerland contain no approval for it, as checked on 6 September 2026. The manufacturer announced that it would apply in the United States in early 2027, but it had not done so.
What is retatrutide?
It is a peptide made in the laboratory, a chain of 39 amino acid building blocks with a fatty acid chain attached that keeps it in the body for longer. From a single molecule it switches on the docking points for three hormones, GIP, GLP-1 and glucagon. The drug company Eli Lilly developed it under the code LY3437943.
How much weight did people lose in the retatrutide trials?
In the mid-stage trial, participants on the highest dose lost an average of 24.2% of their body weight over 48 weeks, against 2.1% on a dummy injection. TRIUMPH-1 reported 28.3% over 80 weeks, but that figure comes from a press release rather than from a scientific journal.
Is retatrutide the same as tirzepatide?
No. Tirzepatide acts on two hormone docking points and is approved in many countries. Retatrutide acts on a third one as well, for glucagon, and is approved in none. The trial that compares the two directly has not reported its results.
What are the most common retatrutide side effects?
Nausea, diarrhoea, constipation and vomiting, all of which get more common at higher doses. In TRIUMPH-1, nausea affected 42.4% of the highest-dose group against 14.8% of those on placebo. Odd skin sensations such as tingling or numbness have also been reported, as has a pulse that rises with the dose.
Does retatrutide prevent heart attacks or strokes?
No trial has shown that. In TRIUMPH-3 the heart figures came with ranges wide enough to include no difference at all, so they settle nothing. The trial built to answer the question enrols 10,000 people and will not finish before February 2029.
Why does this page list retatrutide doses?
Because those doses are simply facts about the studies, published in the cited trials and named in the manufacturer's own announcements. They describe what was given inside supervised trials that had medical monitoring and rules for stopping. They are not instructions for anyone to follow.
Is retatrutide banned in sport?
Yes, at all times. Category S0 of the 2026 prohibited list covers every substance that no health authority currently approves, including those still being tested. Retatrutide falls under it because of that status, not because it is named on the list.
Have the retatrutide phase 3 results been peer-reviewed?
Not as of 6 September 2026. TRIUMPH-1 to TRIUMPH-4 exist only as announcements from the manufacturer. The independently reviewed record stops at the mid-stage trials and the early work that came before them.
What is still unknown about retatrutide?
Whether it actually prevents heart attacks, strokes or kidney failure, whether it is safe over many years, and whether the effect lasts beyond the length of the trials. No authority has weighed its benefits against its risks, and nothing keeps track of side effects in people who use it outside a trial.
Sources
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- Eli Lilly and Company. Press release, 21 May 2026, TRIUMPH-1 topline results. https://www.prnewswire.com/news-releases/lillys-triple-agonist-retatrutide-delivered-powerful-weight-loss-in-pivotal-phase-3-obesity-trial-302778859.html
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Cite this page
Facts on this page were verified on 6 September 2026, and every register query behind the status table was run on that date. Pages about substances in active development age quickly, so the version and date matter as much as the content.
myPeptides Research & Editing. (2026). Retatrutide: what the trials show, status and safety. Version 1.0, 6 September 2026. myPeptides Peptide Register. Retrieved from https://mypep.app/peptides/retatrutide
How pages in this register are compiled and graded is described under methodology; the full register is at peptides.
| Version | Date | Change |
|---|---|---|
| 1.0 | 2026-09-06 | Initial publication |
Last verified: 6 September 2026. Next review: on publication of a peer-reviewed phase 3 report, on submission of a marketing application, or on any change in the anti-doping classification.