What Is Retatrutide?
A clear, cited overview of retatrutide: what it is, how it works, its weight-loss results and side effects, how it is taken, and whether it is FDA approved.
Retatrutide is one of the most talked-about investigational weight-loss medicines, but solid, plain-language information can be hard to find. This page summarizes what published trials and Eli Lilly have actually reported. It is general educational information, not medical advice, and retatrutide is not FDA-approved.
What is retatrutide?
Retatrutide (development code LY3437943, sometimes shortened to "reta") is an investigational once-weekly injectable medicine developed by Eli Lilly. Chemically it is a synthetic 39-amino-acid peptide. It is being studied primarily for chronic weight management and type 2 diabetes. It has not been approved by the FDA and is not available by prescription.
How does retatrutide work?
Retatrutide is a triple agonist: a single molecule that activates three receptors at once, the GLP-1, GIP, and glucagon receptors. GLP-1 and GIP are the incretin pathways already used by medicines like semaglutide and tirzepatide, while the added glucagon activity is thought to increase energy expenditure. A fatty-acid chain gives retatrutide a half-life of roughly 6 days, which supports once-weekly dosing.
What is retatrutide used for?
Retatrutide is still in trials, so it has no approved use yet. Its Phase 3 program studies it for obesity and overweight (the TRIUMPH program) and type 2 diabetes (the TRANSCEND-T2D program), and one trial (TRIUMPH-4) also looked at people with obesity and knee osteoarthritis. Any use outside a clinical trial is not an approved indication.
Retatrutide and weight loss
Weight loss is what drew attention to retatrutide. In its Phase 2 obesity trial, published in the New England Journal of Medicine, the 12 mg once-weekly dose produced a mean weight reduction of about 24.2% at 48 weeks, with roughly a quarter of participants on the top dose losing more than 30% of their body weight. In the Phase 3 TRIUMPH-1 trial reported in 2026, the 12 mg dose produced about 28.3% mean weight loss at 80 weeks, with roughly 45% of that group losing at least 30% of their body weight; the lower 4 mg dose produced about 19% weight loss. These are trial averages, and individual results vary widely.
Retatrutide side effects
As with other incretin-based medicines, the most common side effects reported in trials were gastrointestinal, including nausea, diarrhea, vomiting, and constipation, mostly during dose escalation. Trials also reported a dose-dependent increase in heart rate that, in Phase 2, peaked around 24 weeks and then declined. Because retatrutide is investigational, its complete safety profile is still being characterized in ongoing trials. This is not a full list of possible effects.
How is retatrutide taken?
In trials, retatrutide is given as a once-weekly subcutaneous injection, started at a low dose and increased gradually over time (Phase 2 studied 1, 4, 8, and 12 mg weekly). Escalating slowly is intended to reduce gastrointestinal side effects. Only a qualified prescriber can determine an appropriate dose for an individual, and retatrutide is not currently available by prescription. This page does not provide dosing recommendations.
Is retatrutide FDA approved?
No. As of 2026, retatrutide is not approved by the FDA. It is completing its Phase 3 program, and Eli Lilly is expected to file for regulatory review afterward, so approval, if it comes, would be later. Until then it cannot be prescribed as an approved medicine, and anything sold as "retatrutide" outside a formal clinical trial is not FDA-approved and may carry safety and quality risks.
Is retatrutide a peptide?
Yes. Retatrutide is a synthetic peptide, which is why many people search for the "retatrutide peptide." Our retatrutide peptide guide goes deeper into the chemistry and how people track it.
Tracking a retatrutide routine
If you and your healthcare provider have decided on a weekly routine, a clean record helps you stay consistent. RetaPal is a private retatrutide tracker: log each weekly dose in one tap, count down to your next injection, set optional reminders, and record hunger check-ins, all stored only on your device. It never recommends, calculates, or suggests a dose, you simply log the dose you took.
Retatrutide FAQ
What is retatrutide in simple terms?
Retatrutide is an investigational once-weekly injectable medicine from Eli Lilly, being studied mainly for weight management and type 2 diabetes. It is a synthetic peptide that acts on three appetite- and metabolism-related receptors at once. As of 2026 it is not FDA approved.
How much weight loss does retatrutide cause?
In its Phase 2 obesity trial, the 12 mg weekly dose produced about 24.2% mean weight loss at 48 weeks. In the Phase 3 TRIUMPH-1 trial reported in 2026, the 12 mg dose produced about 28.3% mean weight loss at 80 weeks, with roughly 45% of that group losing at least 30% of their body weight. Individual results in practice vary and depend on many factors.
What are the side effects of retatrutide?
The most common side effects reported in trials were gastrointestinal: nausea, diarrhea, vomiting, and constipation, mostly during dose escalation. Trials also noted a dose-dependent, generally transient increase in heart rate. Because retatrutide is still investigational, its full safety profile is still being characterized.
How is retatrutide taken?
In clinical trials, retatrutide is given as a once-weekly subcutaneous injection, started at a low dose and increased gradually. Its roughly 6-day half-life is what supports weekly dosing. Only a prescriber can determine an appropriate dose, and retatrutide is not currently available by prescription.
Is retatrutide FDA approved?
No. As of 2026 retatrutide is investigational and not approved by the FDA. It is completing Phase 3 trials, with a regulatory submission expected afterward. It cannot be prescribed as an approved medicine, and products sold as "retatrutide" outside a clinical trial are not FDA approved.
References
The figures on this page are drawn from the primary sources below and reflect published trials and Eli Lilly disclosures as of 2026.
- Retatrutide Phase 2 obesity trial (Jastreboff et al., 2023) — New England Journal of Medicine
- Retatrutide mechanism, structure, and half-life — Eli Lilly Medical
- TRIUMPH-1 Phase 3 obesity topline results (2026) — Eli Lilly
- TRIUMPH-4 Phase 3 obesity and osteoarthritis results — Eli Lilly
- Retatrutide first Phase 3 type 2 diabetes trial results — Eli Lilly
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Track your weekly retatrutide routine
RetaPal logs every dose, counts down to your next injection, and keeps it all private on your device. It never recommends or calculates doses.
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