Retatrutide
Retatrutide switches on three gut-hormone receptors: GIP, GLP-1 and glucagon. It is an investigational weekly injection from Eli Lilly and is not approved.
Retatrutide (formerly LY3437943)
Also searched as: reta, LY3437943, retatrutide FDA, ritatrutide.
Educational information. This page does not give dosing instructions or tell you what to take. Ask a prescriber about your own care.
In plain English
Retatrutide is a lab-made molecule that activates three receptors your body's own hormones use. Two of them, GLP-1 and GIP, are released after meals and help control appetite and blood sugar. Tirzepatide already uses those two. Retatrutide adds a third, the glucagon receptor. Glucagon is a hormone that tells the liver and fat tissue to burn stored energy, and researchers think that may add to the weight loss.
It is given as a weekly injection under the skin. Eli Lilly, the maker, has reported results from large phase 3 trials in adults with obesity. Two of them are now published in major journals, and in those trials people lost more weight on retatrutide than on placebo, with the most common side effects affecting the stomach and gut. Two further trials in adults with sleep apnea, published in October 2026, found larger drops in breathing interruptions than placebo. See {{route:sleep-apnea|sleep apnea and weight-loss medicines}}.
It is not an approved medicine anywhere. Lilly has said it plans to submit it to the FDA in the first quarter of 2027. Names you may see online, such as reta, LY3437943 and ritatrutide, all point to this same drug. Products sold under those names outside a clinical trial are not FDA-approved and have not been checked by the FDA.
Brand names and products
A generic name identifies the drug itself. A brand name identifies one company's product. One drug can come in several products with different forms and approved uses, so the brand name often tells you more about what a prescription is for.
No brand name is recorded for this medicine because there is no approved product.
Approved and investigational. Every use of retatrutide is investigational. There is no approved product.
How it works
Retatrutide is a single peptide designed to activate the GIP, GLP-1 and glucagon receptors together. GIP and GLP-1 activity is linked to lower appetite, slower stomach emptying and better insulin release. Glucagon receptor activity is thought to raise energy use and reduce fat in the liver. How much each of the three receptors contributes to the effect in people is still being worked out.
Forms and approval status
| Form | How it is taken | U.S. status |
|---|---|---|
| Retatrutide injection (investigational) | Once weekly in trials. Only available inside clinical trials or a sponsor-run expanded-access program. Anything else sold under this name is not a regulated medicine. | Not approved anywhere. Phase 3 obesity results are published (TRIUMPH-1 and TRIUMPH-2). Lilly stated on July 23, 2026 that it plans to submit retatrutide to the FDA in the first quarter of 2027. An expanded-access program is listed on ClinicalTrials.gov. |
What the trials found
These are group averages from published trials in adults without diabetes unless stated. See how to read trial numbers before comparing.
Retatrutide phase 2 (obesity)
Average change in body weight. Every bar uses one scale, 0 to 25 percent.
- People studied
- 338 adults with obesity, or overweight plus at least one weight-related condition
- Length
- 48 weeks
- Compared with
- Placebo once weekly. Some dose groups started at 2 mg and others at 4 mg, to compare starting amounts
- What was measured
- Average change in body weight at week 48
- Analysis approach
- Least-squares mean change from baseline, as reported in the abstract
- Other results
- At 24 weeks, the primary endpoint, the average change was -7.2% (1 mg), -12.9% (4 mg), -17.3% (8 mg) and -17.5% (12 mg) vs -1.6% with placebo. At 48 weeks, weight loss of at least 15% occurred in 60% (4 mg), 75% (8 mg) and 83% (12 mg) of participants vs 2% with placebo.
- Safety
- The most common side effects were gastrointestinal, increased with dose, were mostly mild to moderate, and were partly reduced by the lower 2 mg starting amount. Heart rate rose in a dose-dependent way, peaked at 24 weeks and declined afterward.
- Limits
- Phase 2 trial with 338 participants, so it was not built to settle rare side effects. Funded by the manufacturer. Group averages do not predict one person's result.
Sources: Jastreboff AM 2023
TRIUMPH-1
Average change in body weight. Every bar uses one scale, 0 to 25 percent.
- People studied
- 2,339 adults with obesity, or overweight plus a weight-related condition, without diabetes
- Length
- 80 weeks
- Compared with
- Placebo once weekly
- What was measured
- Average change in body weight at week 80
- Analysis approach
- Treatment-regimen estimand: effects regardless of treatment discontinuation
- Other results
- Among participants with knee osteoarthritis, knee pain scores (1 to 10 scale) fell by 3.4, 3.9 and 4.1 points across the three doses vs 2.5 with placebo. Among participants with obstructive sleep apnea, breathing interruptions fell by 22.8, 34.3 and 32.1 events per hour vs 9.6 with placebo.
- Safety
- The most common side effects were gastrointestinal. The abstract does not give percentages for them, so see the full paper.
- Limits
- Funded by the manufacturer. Participants did not have diabetes. Sponsor press releases quote larger numbers because they use a different calculation, so the figures differ. Group averages do not predict one person's result.
Sources: Jastreboff AM 2026, TRIUMPH-1 trial record (NCT05929066)
TRIUMPH-2
Average change in body weight. Every bar uses one scale, 0 to 25 percent.
- People studied
- 1,152 adults with obesity and type 2 diabetes
- Length
- 80 weeks
- Compared with
- Placebo once weekly, added to the participants' existing diabetes treatment
- What was measured
- Average change in body weight at week 80
- Analysis approach
- Treatment-regimen estimand: effects regardless of treatment discontinuation
- Other results
- Differences from placebo were -6.9, -11.8 and -13.8 percentage points across the three doses.
- Safety
- Diarrhea: 27%, 34% and 34% across the three doses vs 13% with placebo. Nausea: 14%, 21% and 28% vs 8%. Low blood pressure and abnormal skin sensations (dysesthesia) were also more frequent than with placebo. Stopping treatment because of side effects or death: 4%, 12% and 8% vs 5%. Deaths: 2, 3 and 1 across the three doses vs 1 with placebo, all judged unrelated to the study drug by the investigators.
- Limits
- Funded by the manufacturer. Participants all had type 2 diabetes and were already on stable treatment, so results may not match people without diabetes. Group averages do not predict one person's result.
Sources: Bellido V 2026
Safety
No FDA label exists for this medicine yet. The information below comes from published trial reports. The points below are a summary and may be incomplete.
Boxed warning and label notes
- Retatrutide injection (investigational): Not applicable. Not approved.
Warnings labels describe
- Not approved, so no official label exists. Safety information is limited to trial reports.
- Trial participants were screened and monitored. Results from a supervised trial do not carry over to products bought outside a trial.
Most common in trials
- Diarrhea
- Nausea
- Constipation
- Decreased appetite
- Vomiting
- Abnormal skin sensations (dysesthesia)
- Low blood pressure
- Faster heart rate (phase 2)
Less common but serious
- In TRIUMPH-2, 4% to 12% of people on retatrutide stopped treatment because of side effects or death (5% on placebo). The investigators judged all deaths unrelated to the drug.
- No full list of serious side effects is in this atlas yet. That will come from the full trial papers and, if approved, the official label.
What is still unknown
- Long-term safety beyond about 80 weeks, and what happens to weight and heart rate after stopping.
- The final approved indication, dose and dose-escalation steps. These are set by regulators, not by trial reports.
- How it compares directly with tirzepatide. A head-to-head phase 3 trial is registered (NCT06662383) but its results are not published.
- Whether trial results hold for people who differ from those enrolled, and how the third receptor (glucagon) affects heart rate and the liver over years.
- Results from the other trials Lilly has announced (for example TRIUMPH-3 in people with severe obesity and heart disease) are so far company statements, not peer-reviewed papers.
Compiled from public information: FDA-approved labels, manufacturer websites, ClinicalTrials.gov and published journal articles. Sources are listed at the bottom of this page.
Sources
- Lilly's triple agonist retatrutide successful in two additional phase 3 trials (TRIUMPH-2 and TRIUMPH-3) Eli Lilly and Company investor news release, July 23, 2026. Company statement, not peer reviewed. Trade press, secondary source
- Retatrutide once weekly for treatment of obstructive sleep apnea (TRIUMPH-1-OSA and TRIUMPH-2-OSA) Grunstein RR, et al. N Engl J Med. Published October 20, 2026. Presented at the 28th Congress of the European Sleep Research Society. Funding: Eli Lilly. Summarized from the abstract on NEJM.org. A PubMed record was not yet available on October 21, 2026. Journal article
- Pre-approval expanded access of retatrutide (NCT07629401) ClinicalTrials.gov identifier NCT07629401. Sponsor: Eli Lilly and Company. Trial registry
- ClinicalTrials.gov U.S. National Library of Medicine. Trial registry
- Triple-hormone-receptor agonist retatrutide for obesity, a phase 2 trial Jastreboff AM, et al. N Engl J Med. 2023;389(6):514-526. PMID 37366315. Funding: Eli Lilly. Journal article
- Retatrutide, a triple hormone receptor agonist, for treatment of obesity (TRIUMPH-1) Jastreboff AM, et al. N Engl J Med. Published September 29, 2026. PMID 42814954. Funding: Eli Lilly. Journal article
- Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2) Bellido V, et al. Lancet. 2026;408(10563):1455-1472. PMID 42810372. Funding: Eli Lilly. Journal article
- TRIUMPH-1 trial record (NCT05929066) ClinicalTrials.gov identifier NCT05929066. Trial registry