TRIUMPH-1 is retatrutide's pivotal Phase 3 obesity trial — 2,339 adults with obesity or overweight (without diabetes), followed for 80 weeks. Topline results arrived May 21, 2026, with full results presented at the American Diabetes Association meeting in June. The headline: 28.3% average weight loss at 80 weeks on the 12 mg dose (efficacy estimand), the largest Phase 3 average reported for an obesity medication. [1]
The full dose table
| Dose | Mean weight loss at 80 weeks (efficacy estimand) |
|---|---|
| 12 mg | 28.3% (−70.3 lbs) |
| 9 mg | 25.9% (−64.4 lbs) |
| 4 mg | 19.0% (−47.2 lbs) |
| Placebo | 2.2% (−5.5 lbs) |
All figures from Lilly's topline release. [1]
How deep the losses ran
The distribution matters as much as the average — these are the shares of participants reaching each threshold at 80 weeks: [1]
| Threshold | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| ≥25% weight loss | 27.8% | 52.9% | 62.5% | 2.2% |
| ≥30% weight loss | 15.3% | 37.9% | 45.3% | 0.5% |
| ≥35% weight loss | 5.9% | 20.8% | 27.2% | 0.3% |
Two more measures from the same release: 65.3% of participants on 12 mg finished with a BMI under 30 — below the obesity threshold — including 37.5% of those who started with class 3 obesity (BMI ≥40); and waist circumference fell by 24.1 cm (12 mg) versus 3.6 cm on placebo, from a baseline of 118.3 cm. [1]
Two results deserve as much attention as the average:
- Deep responders. 45.3% of participants on 12 mg lost 30% or more of their body weight. [1] That share of a trial population reaching bariatric-surgery-range weight loss on a medication is new territory.
- The extension. Among participants with BMI ≥35 who continued, average weight loss reached 30.3% (85.0 lbs) at 104 weeks — suggesting the effect deepens, rather than rebounds, into a second year. [1]
Estimands: why you'll see two different sets of numbers
Trial results come in two statistical flavors, and mixing them is the most common error in coverage of this drug:
- The efficacy estimand asks: what happens if participants stay on treatment as intended? That's the 28.3% figure.
- The treatment-regimen estimand counts everyone randomized, including people who stopped the drug. It always runs lower. The peer-reviewed NEJM publication (September 29, 2026) reports TRIUMPH-1 as 17.6% / 23.7% / 25.0% across the three doses versus 3.9% for placebo under this analysis. [2]
Both are legitimate; they answer different questions. When you compare retatrutide to other drugs' trials, make sure you're comparing the same estimand — and even then, remember these are different trials with different populations.
Side effects in TRIUMPH-1
The common adverse events are the GI effects familiar from every incretin drug: nausea, diarrhea, constipation, decreased appetite, vomiting. The notable new finding is dysesthesia — abnormal skin sensations — which was not reported in Phase 2:
| Dose | Dysesthesia incidence |
|---|---|
| 4 mg | 5.1% |
| 9 mg | 12.3% |
| 12 mg | 12.5% |
| Placebo | 0.9% |
Lilly describes the events as generally mild to moderate and says most resolved. [1] [3] The signal recurs in the other TRIUMPH trials, so it will get regulatory attention — our side-effects article covers it across the whole program.
How TRIUMPH-1 compares to what came before
Phase 2 (NEJM, 2023) showed roughly 24.2% at 48 weeks on the highest dose in a smaller population. [4] TRIUMPH-1 confirms, extends and deepens that result in a pivotal-scale trial twice as long. With TRIUMPH-2, -3 and -4 also positive, Lilly says the data package for global submissions is complete, with a U.S. FDA submission planned for Q1 2027. [5]
The live regulatory picture is on the FDA approval tracker.