For two years the most quoted number in this field was 24.2%, the mean weight change at the top dose of retatrutide in a phase 2 trial published in 2023. That number is now out of date. Between May and July 2026 Eli Lilly reported topline results from three phase 3 trials of the molecule, and the picture is both larger and more complicated than the one figure suggested.
TRIUMPH-1: obesity without diabetes
Reported May 21, 2026. The trial randomized 2,339 adults with obesity or overweight and at least one weight-related condition, none of them with diabetes. Mean starting weight was 112.7 kg and mean BMI was 40.0. The primary analysis was at 80 weeks.
Mean weight change at 80 weeks:
| Arm | Mean change | Absolute |
|---|---|---|
| Retatrutide 4 mg | −19.0% | −21.4 kg |
| Retatrutide 9 mg | −25.9% | −29.2 kg |
| Retatrutide 12 mg | −28.3% | −31.9 kg |
| Placebo | −2.2% | −2.5 kg |
At 12 mg, 62.5% of participants lost at least a quarter of their body weight and 45.3% lost at least 30%, against 2.2% and 0.5% on placebo.
The tolerability figures sit next to those. Discontinuations because of adverse events were 4.1% at 4 mg, 6.9% at 9 mg and 11.3% at 12 mg, versus 4.9% on placebo. At the top dose, 42.4% reported nausea (14.8% on placebo), 32.0% diarrhea (13.5%), 25.3% vomiting (4.8%), and 12.5% dysesthesia, an abnormal skin sensation, against 0.9% on placebo. A 104-week blinded extension that pushed the 12 mg group to the maximum tolerated dose reached a mean of −30.3% in 532 participants whose starting BMI was 35 or higher.
TRIUMPH-2 and TRIUMPH-3
Both reported in July 2026.
TRIUMPH-2 enrolled 1,152 adults with type 2 diabetes and obesity or overweight. Mean weight change at 80 weeks was −12.7%, −19.1% and −20.8% across the three doses, against −4.0% on placebo. HbA1c fell by 1.4 to 1.6 percentage points, against 0.2 on placebo. People with type 2 diabetes have lost less weight than people without it in every incretin trial to date, and this one held to the pattern.
TRIUMPH-3 enrolled 1,949 adults with a BMI of 35 or higher and established cardiovascular disease. The 9 mg and 12 mg arms reached −21.6% and −22.6% at 80 weeks, against −3.2% on placebo.
What the numbers do and do not say
Lilly has said it plans to submit the drug to the FDA in the first quarter of 2027. Until a review concludes, retatrutide is available only to people enrolled in its trials. No retatrutide product is approved for any use, anywhere.
The comparison everyone will make is with the two approved incretins. In STEP-1, semaglutide produced a mean change of −14.9% at 68 weeks. In SURMOUNT-1, tirzepatide produced −20.9% at 72 weeks. Those trials enrolled different populations over different durations, so the gap to −28.3% is indicative, not a head-to-head result. The only direct comparisons will come from trials designed to make them.
Two things in the data are easy to skip. The first is that the dose with the largest effect also had the highest dropout rate, roughly one participant in nine, and a side-effect profile that most of the trial population tolerated but a meaningful minority did not. The second is that the 104-week figure comes from a subgroup selected for a high starting BMI, which is where percentage losses are typically largest. Both are ordinary features of a real trial, and neither appears in the headline.
Sources: Eli Lilly topline announcements for TRIUMPH-1 (May 21, 2026) and TRIUMPH-2 and TRIUMPH-3 (July 2026); HCPLive coverage of the same releases; Jastreboff et al., NEJM 2023 (phase 2); Wilding et al., NEJM 2021 (STEP-1); Jastreboff et al., NEJM 2022 (SURMOUNT-1).
For research use only · Not for human or veterinary use · No compound discussed here is FDA-approved for any indication