Retatrutide is the most-searched medicine that does not yet exist as a medicine. Its trial results are large, its approval is at least a year away, and its name is on vials FDA has sent warning letters about. This page reports where it stands on 2026-09-05: status, the doses the trials used, the results by trial, the safety signal, and what is being sold. It does not recommend anything and it does not advise on use; our editorial standards explain why.
What it is, and where it stands
Retatrutide (LY3437943) is a once-weekly injectable that activates three receptors, GIP, GLP-1 and glucagon; tirzepatide activates the first two. It is not approved anywhere. Lilly's release of 2026-07-23 states that the TRIUMPH-2 and TRIUMPH-3 results complete "the clinical data package to support global submissions" for obesity, knee osteoarthritis pain and obstructive sleep apnea, and that the company "plans to submit a Biologics License Application (BLA) for retatrutide to FDA in Q1 2027" (Lilly). Seven further Phase 3 readouts were expected in 2026, including sleep apnea, low back pain, liver disease and cardiovascular outcomes.
The doses the trials used
| Trial | Doses | Escalation | Duration |
|---|---|---|---|
| Phase 2 (Jastreboff et al., NEJM 2023) | 1 mg, 4 mg, 8 mg, 12 mg once weekly, subcutaneous | 4 mg arms started at 2 or 4 mg; 8 mg arms at 2 or 4 mg; 12 mg arm at 2 mg | 48 weeks; 338 adults |
| TRIUMPH-1, -2, -3, -4 (Lilly releases) | 4 mg, 9 mg, 12 mg once weekly (TRIUMPH-3 and -4: 9 and 12 mg only) | Escalation from a low starting dose over the initial weeks; a maximum-tolerated-dose extension in TRIUMPH-1 | 80 weeks (TRIUMPH-1, -2, -3); 68 weeks (TRIUMPH-4); 104-week extension |
These are the doses Lilly will ask FDA to approve. No label exists, and no dose is approved for any person. The 12 mg weekly figure that appears on research-vendor pages is the trial's top dose transplanted onto an unregulated product; FDA's warning letter to Mile High Compounds quoted exactly that schedule, "up to 12mg weekly", as evidence the seller's product was intended as a human drug (FDA, 2026-03-31).
Results, by trial
| Trial | Population | Weight change vs placebo | Stopped for adverse events |
|---|---|---|---|
| Phase 2, 2023 | 338 adults with obesity | At 24 weeks: −7.2% (1 mg), −12.9% (4 mg), −17.3% (8 mg), −17.5% (12 mg); 24.2% at 48 weeks on 12 mg | Not in the abstract |
| TRIUMPH-1, 2026-05-21 | 2,339 adults without diabetes, 80 weeks | −19.0%, −25.9%, −28.3% vs −2.2% (efficacy estimand); 17.6%, 23.7%, 25.0% vs 3.9% counting everyone; up to −30.3% at 104 weeks in 532 with BMI ≥35 | 4.1%, 6.9%, 11.3% vs 4.9% |
| TRIUMPH-4, 2025-12-11 | 445 adults with knee osteoarthritis, 68 weeks | −26.4% (9 mg), −28.7% (12 mg) vs −2.1%; WOMAC pain −4.5 and −4.4 points vs −2.4 | 12.2%, 18.2% vs 4.0% |
| TRIUMPH-2, 2026-07-23 | 1,152 adults with type 2 diabetes, 80 weeks | −12.7%, −19.1%, −20.8% vs −4.0%; A1C down up to 1.6 points | 3.8%, 11.6%, 7.7% vs 4.9% |
| TRIUMPH-3, 2026-07-23 | 1,949 adults with severe obesity and cardiovascular disease, 80 weeks | −21.6% (9 mg), −22.6% (12 mg) vs −3.2% | 9.8%, 13.5% vs 4.8% |
Sources: Lilly's releases of 2025-12-11, 2026-05-21 and 2026-07-23. Only the phase 2 trial is a peer-reviewed paper; every Phase 3 figure is a company release awaiting publication. The most common adverse events in TRIUMPH-1 at 12 mg versus placebo were nausea (42.4% vs 14.8%), diarrhea (32.0% vs 13.5%), constipation (26.1% vs 10.9%) and vomiting (25.3% vs 4.8%). The pattern across trials is more weight loss than the tirzepatide trials reported and a higher rate of stopping at the top dose, from 7.7% in people with diabetes to 18.2% in the knee-osteoarthritis trial.
What is being sold under the name
Research-chemical vendors sell vials labeled retatrutide under research-use-only disclaimers. FDA's warning letters naming retatrutide run from Summit Research Peptides and Prime Peptides (2024-12-10) through Gram Peptides, Pink Pony Peptides, Prime Sciences and Mile High Compounds (2026-03-31) to NuScience, Peak Performance, Royal, Tex Peptides and Peptide Partners (2026-08-24), each citing sections 301(d) and 505(a) of the Food, Drug, and Cosmetic Act and each rejecting the research-use disclaimer on the basis of the seller's own marketing. Those letters, with FDA's wording, are tracked on Peptifact. Whether a given vial contains retatrutide, at what purity, has not been checked by any regulator; FDA's Green List import alert of September 2025 admits GLP-1 active ingredients only from inspected facilities, and the research-chemical channel is outside it.
Cost
None, because it cannot lawfully be sold as a medicine. Lilly has not indicated a price. For comparison, Zepbound's self-pay price through LillyDirect was $299 to $449 per month on 2026-09-05; our cost page has every current GLP-1 price.
What is not known
Whether the Phase 3 results hold up in peer review; what the cardiovascular-outcomes trial will show; what the glucagon activity does to heart rate and liver measures over years; what FDA will approve, at which doses, for which indications; and what it will cost. Our comparison with tirzepatide sets out why the trial numbers cannot yet be read against the approved drug's.
Sources and dates
Opened 2026-09-05: Jastreboff et al., NEJM 2023 (PMID 37366315); Lilly's TRIUMPH releases of 2025-12-11, 2026-05-21 and 2026-07-23; FDA's warning letter to Mile High Compounds (2026-03-31) and the letters tracked on Peptifact; FDA's Green List press release (2025-09-05); Lilly's Zepbound coverage and savings page. Corrections go to the contact page.