LY3437943 · GLP-1 / GIP / glucagon · Phase 3 · Eli Lilly
Retatrutide: the evidence-based guide to Lilly's triple agonist.
Retatrutide (LY3437943) is the first GLP-1 / GIP / glucagon triple agonist in late-stage development. Here's what the science actually says — every claim cited, every number from the primary literature.
−24.2%
mean body-weight reduction at 48 weeks on the 12 mg dose — the largest reported for any obesity drug in a published trial
- Dose
- 12 mg weekly
- Duration
- 48 weeks
- Participants
- N = 338
- Comparator
- Placebo −2.1%
At a glance
- Generic name
- Retatrutide
- Code name
- LY3437943
- Manufacturer
- Eli Lilly
- Drug class
- GLP-1 / GIP / glucagon triple agonist
- Route
- Once-weekly subcutaneous
- Phase
- Phase 3 (TRIUMPH program)
- FDA status
- Investigational — not approved
- Earliest US approval
- Projected 2026–2027
The basics
What is retatrutide?
Retatrutide is an experimental medication for obesity and type 2 diabetes developed by Eli Lilly. It is administered by a once-weekly subcutaneous injection, similar to Ozempic, Wegovy, Mounjaro, and Zepbound. What makes retatrutide different is that it activates three hormone receptors at once instead of one or two — GLP-1, GIP, and glucagon.
In a Phase 2 trial published in the New England Journal of Medicine in 2023, adults with obesity who took the highest tested dose lost an average of 24.2% of their body weight over 48 weeks. For comparison, that is roughly the same magnitude of weight loss typically seen after bariatric surgery, and meaningfully larger than what has been reported for tirzepatide or semaglutide in their pivotal obesity trials.
Retatrutide is currently in Phase 3clinical trials under the "TRIUMPH" program. It is not approvedfor sale in any country, and any product marketed online as "retatrutide for sale" is unregulated and not the same molecule that's being studied in trials.
How does it compare?
Retatrutide vs. tirzepatide vs. semaglutide
| Property | Retatrutide | Tirzepatide | Semaglutide |
|---|---|---|---|
| Drug class | GLP-1 / GIP / glucagon | GLP-1 / GIP | GLP-1 |
| Brand names | — (investigational) | Mounjaro · Zepbound | Ozempic · Wegovy |
| Avg. weight loss at 48 wk* | ≈ 24% | ≈ 21% | ≈ 15% |
| Dosing | Once weekly SC | Once weekly SC | Once weekly SC |
| FDA status (US) | Phase 3 | Approved | Approved |
*Approximate placebo-adjusted weight loss at the highest tested doses across separate Phase 2/3 trials. Not a head-to-head comparison. Sources: NEJM 2023 (retatrutide), SURMOUNT-1 (tirzepatide), STEP 1 (semaglutide).
Phase 2 obesity trial · 48 weeks
What the trial data shows
In Lilly's Phase 2 obesity trial (Jastreboff et al., NEJM 2023), participants on the highest dose lost an average of 24.2% of body weight after 48 weeks — among the largest reductions ever recorded for a pharmacologic agent.
Source: Jastreboff AM, et al. Triple Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med 2023; 389:514-526.
Explore the guide
Everything we know about retatrutide
How retatrutide works
Triple agonism of GLP-1, GIP, and glucagon receptors — and why activating all three matters.
Read moreEvidenceTRIUMPH trial program
TRIUMPH-1 through TRIUMPH-4: design, primary endpoints, and reported readouts.
Read moreOutcomesWeight-loss results in detail
Phase 2 obesity outcomes by dose, BMI subgroup, and time on therapy.
Read moreSafetySide effects and tolerability
GI events, heart-rate signal, and how withdrawals compared with placebo.
Read moreDosingDosing in clinical trials
Titration schedules used by Lilly and the rationale for each dose level.
Read moreCompareRetatrutide vs. tirzepatide
Cross-trial comparison of efficacy, side effects, and mechanism of action.
Read moreCompareRetatrutide vs. semaglutide
Where retatrutide's third receptor target may add efficacy beyond GLP-1 alone.
Read moreRegulatoryFDA approval status
Where retatrutide stands with the FDA and EMA, plus realistic launch timelines.
Read moreAccessProjected cost & access
List-price benchmarks vs. tirzepatide and what self-pay channels could look like.
Read moreUpdatesLatest news & readouts
Trial readouts, label submissions, and major retatrutide press from Lilly.
Read moreCommon questions
Retatrutide FAQ
What is retatrutide?
Retatrutide (LY3437943) is an investigational once-weekly injectable medication being developed by Eli Lilly for obesity and type 2 diabetes. It is the first 'triple agonist' in late-stage trials, simultaneously activating the GLP-1, GIP, and glucagon receptors to drive weight loss and improve metabolic markers.
Is retatrutide FDA approved?
No. As of 2026, retatrutide is not approved by the FDA, EMA, MHRA, or any other regulator. It is in Phase 3 clinical trials (the TRIUMPH program). Independent analysts project a possible US launch in late 2026 or 2027 if Phase 3 readouts and the regulatory submission stay on schedule.
How much weight do people lose on retatrutide?
In Lilly's Phase 2 obesity trial published in NEJM (2023), participants on the highest dose of 12 mg lost an average of 24.2% of body weight after 48 weeks. That is the largest mean weight loss reported for any GLP-1-class medication in a published trial to date, though head-to-head studies against tirzepatide have not been completed.
How is retatrutide different from Ozempic, Wegovy, Mounjaro, and Zepbound?
Ozempic and Wegovy contain semaglutide, which targets one receptor (GLP-1). Mounjaro and Zepbound contain tirzepatide, which targets two (GLP-1 and GIP). Retatrutide adds a third target — the glucagon receptor — which appears to increase energy expenditure and contribute to greater weight loss in trials.
What are the side effects of retatrutide?
The most common side effects in trials were gastrointestinal: nausea, diarrhea, vomiting, and constipation, mostly mild-to-moderate and concentrated during dose escalation. A modest, dose-dependent increase in resting heart rate was also observed. The full safety profile is still being characterized in Phase 3 trials.
Where can I get retatrutide?
Retatrutide is not available by prescription anywhere in the world because it has not received regulatory approval. It is only accessible through Lilly's clinical-trial program. Products marketed online as 'research retatrutide' are unregulated, of unverified purity, and may be illegal to import or use in many jurisdictions.
When will retatrutide be approved?
Eli Lilly has indicated that initial Phase 3 readouts from the TRIUMPH program were expected starting in 2025-2026, with potential FDA submission to follow. A US approval decision in late 2026 or during 2027 is the most commonly cited analyst estimate, though regulatory timelines are inherently uncertain.
Stay informed
New trial readouts. Plain-language analysis. No spam.
We summarize every major retatrutide readout, label development, and approval milestone the day it lands.