This treatment is in clinical trials and has not been approved by the FDA or any regulatory authority. It is not available for prescription. Current stage: Phase 3 (TRIUMPH programme) — first Phase 3 result published 2026. Estimated approval: 2027 (estimated — not confirmed) — subject to change.
Retatrutide
Eli Lilly · Code: LY3437943
A triple GIP, GLP-1, and glucagon receptor agonist. The first Phase 3 result (TRIUMPH-4, 2026) showed 28.7% average weight loss at 68 weeks — the highest weight loss ever recorded in a Phase 3 randomised controlled trial. The addition of glucagon receptor agonism on top of GIP and GLP-1 may further boost metabolic rate and fat burning beyond what dual agonists achieve.
Quick read · 4 min
- •Retatrutide is an investigational drug — it has not yet been approved by any regulatory authority
- •Best trial result so far: up to 28.7% average weight loss
- •Current stage: Phase 3 (TRIUMPH programme) — first Phase 3 result published 2026
- •Expected approval: 2027 (estimated — not confirmed) — this is an estimate and not confirmed
Based on clinical trials · No rankings · Every claim linked to source
Last reviewed: April 2026
Why this matters:
Compared to currently approved treatments, this drug is being studied because it may produce significantly greater weight loss than any currently approved medication. These treatments are still under investigation, and results in larger trials may differ from early data.
Development stage and timeline
Current stage:
Phase 3: TRIUMPH programme complete. TRIUMPH-4 results published 2026. TRIUMPH-1, TRIUMPH-2, TRIUMPH-3 data expected 2026.
Next milestone:
FDA decision expected 2027. Not yet approved.
How it works
Activates three receptors simultaneously: GIP (enhances fat storage signalling), GLP-1 (reduces appetite, slows gastric emptying), and glucagon (increases metabolic rate and fat burning). The triple mechanism may produce synergistic weight loss beyond what dual agonists achieve.
Phase 2 trial data by dose
In the Phase 2 trial (where people were randomly assigned to different doses or a dummy pill), participants on different doses lost the following amounts of weight. Phase 3 data is pending.
| Dose | At 24 weeks | At 48 weeks |
|---|---|---|
| 1 mg | –7.2% | –8.7% |
| 4 mg | –12.9% | –17.1% |
| 8 mg | –17.3% | –22.8% |
| 12 mg | –17.5% | –24.2% |
| Placebo | –1.6% | –2.1% |
Phase 3 trial results
In the following Phase 3 trials, participants were randomly assigned to Retatrutide or a dummy pill.
In the TRIUMPH-4 trial, participants lost an average of 28.7% of their body weight at the 12 mg dose (about 71.2 lbs / 32.3 kg on average) — alongside a 75.8% reduction in knee pain. At the 9 mg dose, average weight loss was 26.4%. Placebo: 2.1% weight loss.
Phase 3 programme
- ◆TRIUMPH-4 (published 2026): Adults with obesity and knee osteoarthritis — 28.7% weight loss at 68 weeks
- ◆TRIUMPH-1: Adults with obesity, no type 2 diabetes — data expected 2026
- ◆TRIUMPH-2: Adults with obesity and type 2 diabetes — data expected 2026
- ◆TRIUMPH-3: Adults with Class II/III obesity and established cardiovascular disease — data expected 2026
Side effects (early-stage data)
Frequencies from Phase 2 trial data. Final Phase 3 safety profile may differ.
Notable findings
- ✓28.7% average weight loss at 68 weeks (TRIUMPH-4 Phase 3) — highest ever in a Phase 3 RCT
- ✓75.8% reduction in knee osteoarthritis pain alongside weight loss (TRIUMPH-4)
- ✓Cardiometabolic improvements across blood pressure, lipids, and blood sugar (Phase 2 + Phase 3)
- ✓100% of participants at 8 mg and 12 mg achieved ≥5% weight loss in Phase 2
What this tends to offer vs. what it involves
What this tends to offer
- ✓28.7% average weight loss — highest ever in a Phase 3 trial
- ✓Triple mechanism addresses appetite and metabolism
- ✓75.8% reduction in knee pain in TRIUMPH-4
- ✓Once-weekly injection format
What this involves
- ◆Still under investigation — not yet FDA approved
- ◆Nausea expected similar to or higher than GLP-1 drugs (45% in Phase 2)
- ◆Price and insurance coverage unknown pending approval
- ◆Approval timeline estimates not confirmed
Community insights
These are personal experiences shared in public online communities — not medical advice.
“People following the TRIUMPH-4 trial results described the 28.7% average weight loss figure as 'jaw-dropping' — the highest ever seen in a Phase 3 trial. Many noted it even beat tirzepatide's Phase 3 results.”
“Phase 2 participants described losing weight faster than with Wegovy or Zepbound at similar timepoints. The Phase 3 TRIUMPH-4 data confirmed the effect was real — but the drug is still awaiting FDA approval.”
Sources & references
- [1]Phase 2 randomised controlled trial (NEJM 2023)338 adults with obesity, no type 2 diabetes · 48 weeksAt 12 mg dose: 24.2% mean weight loss at 48 weeks — weight had not plateaued. 100% achieved ≥5% loss; 93% ≥10%; 83% ≥15%. GI side effects consistent with incretin class. Discontinuation: 6–16% across doses.New England Journal of Medicine (2023) ↗
- [2]TRIUMPH-4 Phase 3 trial (published 2026)Adults with obesity and knee osteoarthritis (average BMI 40.4, baseline weight ~112.7 kg) · 68 weeks28.7% mean weight loss at 12 mg dose (about 71.2 lbs average). 26.4% at 9 mg. Knee pain (WOMAC) reduced by 75.8% vs 40.3% placebo. Cardiometabolic improvements including reduced blood pressure and cholesterol. First successful Phase 3 trial.Eli Lilly press release / investor.lilly.com (2026) ↗