What is retatrutide?
Retatrutide, research code LY3437943, is a synthetic peptide being developed by Eli Lilly. It is a triple agonist: a single molecule that activates three hormone receptors at once, GLP-1, GIP and glucagon.
That sets it apart from earlier substances in the same family. Semaglutide (Ozempic, Wegovy) acts on GLP-1 only, and tirzepatide (Mounjaro) on GLP-1 and GIP. Retatrutide adds the glucagon receptor, which is why it is studied as a next-generation substance in obesity and metabolic research.
Key facts
- Code: LY3437943
- Developer: Eli Lilly
- Mechanism: GLP-1, GIP and glucagon receptor agonist
- Half-life: about 6 days (given once weekly in the trials)
- Status: in phase 3 trials, not approved as a medicine
How does triple agonism work?
The three receptors affect metabolism in different ways, and the idea behind retatrutide is that the effects reinforce each other:
- GLP-1: reduces appetite through the brain's satiety centre, slows gastric emptying and stimulates insulin release when blood sugar is high.
- GIP: improves insulin sensitivity and influences how adipose tissue stores and releases energy.
- Glucagon: increases energy expenditure and fat oxidation in the liver. This is what separates retatrutide from tirzepatide.
The glucagon component also explains the strong effects on liver fat seen in the trials.
Research results: phase 2 and phase 3
Phase 2 – obesity (NEJM, 2023)
In the phase 2 trial in people with obesity without diabetes (338 participants, 48 weeks), the highest dose, 12 mg, produced an average weight loss of 24.2%, compared with 2.1% for placebo. The result was published in the New England Journal of Medicine in 2023 and was at the time the highest reported for a substance in the class.
Phase 2 – type 2 diabetes (Lancet, 2023)
A parallel phase 2 trial in people with type 2 diabetes showed clear reductions in long-term blood sugar (HbA1c) and a weight loss of just under 17% after 36 weeks at the highest dose.
Liver fat
In a sub-study, liver fat fell by more than 80% at the higher doses, and liver fat normalised completely in a majority of participants. This has made retatrutide of interest for fatty liver (MASLD) research as well.
Phase 3 – TRIUMPH-1 (2026)
Phase 3 results, published in NEJM
- 2,339 participants, 80 weeks
- –28.3% average weight loss at 12 mg (almost 32 kg), versus –2.2% on placebo
- –19% at 4 mg
- 45% of participants on the highest dose lost more than 30% of their body weight
Eli Lilly presented the first TRIUMPH-1 results in May 2026. The full trial was published in the New England Journal of Medicine on 29 September 2026 (“Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity”, ClinicalTrials.gov NCT05929066). It also reported reduced pain in participants with knee osteoarthritis and fewer apnoea events in participants with sleep apnoea. The most common adverse events were gastrointestinal.
TRIUMPH-2 and TRIUMPH-3 (2026)
Two further phase 3 trials were reported in July 2026. In TRIUMPH-2, in people with type 2 diabetes and overweight, the highest dose gave around 21% weight loss after 80 weeks. In TRIUMPH-3, in people with obesity and cardiovascular disease, weight loss was around 23% at the highest dose. Eli Lilly has said it plans to file for approval with the US FDA in the first quarter of 2027.
Doses tested in the trials
The figures below describe what has been tested in clinical trials. They are research data, not recommendations.
| Trial | Doses (once weekly) | Duration |
|---|---|---|
| Phase 2, obesity | 1, 4, 8 and 12 mg | 48 weeks |
| Phase 2, type 2 diabetes | 0.5–12 mg | 36 weeks |
| Phase 3, TRIUMPH-1 | 4 and 12 mg | 80 weeks |
In the trials the dose was escalated in steps over several weeks to limit gastrointestinal side effects. Retatrutide is supplied as freeze-dried powder and must be reconstituted before laboratory use.
Reported side effects
The side-effect profile in the trials resembles other GLP-1-based substances, but is dose-dependent:
- Gastrointestinal: nausea, vomiting, diarrhoea and constipation were most common, mainly during dose escalation.
- Heart rate: a dose-dependent increase in resting heart rate was reported in phase 2.
- Discontinuation: in TRIUMPH-1, 11% of participants on 12 mg stopped because of side effects. At 4 mg, discontinuations were no higher than in the placebo group.
Retatrutide vs tirzepatide vs semaglutide
| Property | Retatrutide | Tirzepatide | Semaglutide |
|---|---|---|---|
| Receptors | GLP-1 + GIP + glucagon | GLP-1 + GIP | GLP-1 |
| Weight loss, highest dose | ~28% (80 wk, phase 3) | ~21% (72 wk) | ~15% (68 wk) |
| Status | Phase 3, not approved | Approved (Mounjaro) | Approved (Ozempic, Wegovy) |
The trials were run in different populations over different lengths of time, so the figures cannot be compared directly. A deeper look at the dual agonist is in our tirzepatide research guide.
Is retatrutide approved?
No. Retatrutide is not approved by the EMA or by any national medicines agency in the EU, and there is no approved medicine containing it. The peptide sold in Europe today is sold as a research chemical, strictly for laboratory and research use and not for use in humans or animals.
Buying retatrutide for research: what to check
Quality varies widely between suppliers. Always check:
- Purity and analysis: the supplier should be able to show an HPLC analysis for the current batch.
- Amount per vial: compare the price per mg, not the price per pack.
- Form: the peptide should be supplied as freeze-dried (lyophilised) powder, which is stable until reconstituted.
- Shipping and storage: short transit times are an advantage. Unopened powder is best kept frozen at −20 °C.
Retatrutide at Retatrutidebutiken
- Retatrutide 10 mg – 999 SEK, HPLC-tested batch
- Multi-packs down to 78 SEK per mg, see retatrutide prices and stock
- Ships from our warehouse in Sweden
- Certificates by lot number: certificates page
Summary
Retatrutide is the first triple agonist of GLP-1, GIP and glucagon and has shown the largest weight loss so far for its class in both phase 2 and phase 3. It remains under clinical investigation and is not approved as a medicine.
Products are sold for research and laboratory use only and are not intended for humans or animals.