Retatrutide Weight Loss Results: What the Trials Really Show

In Lilly's TRIUMPH-1 trial, adults with obesity lost an average of 28.3% of their body weight after 80 weeks on the highest dose of retatrutide, 12 mg. That's the number behind the headlines. The peer-reviewed paper, which counts everyone assigned to the drug including people who stopped, puts the same group at 25.0%. Both are real; they answer slightly different questions. For how it compares with Zepbound, see retatrutide vs tirzepatide.

Across five successful Phase 3 trials, retatrutide has produced the largest average weight loss seen so far with an obesity drug. It is still investigational and not approved by FDA. Here are the results trial by trial, and what they don't prove.

People with type 2 diabetes consistently lose less weight on incretin drugs than people without it, which is why TRANSCEND-T2D-1 and TRIUMPH-2 look smaller. It's the same pattern seen with semaglutide and tirzepatide.

TRIUMPH-1 is the main obesity trial. Participants started at 2 mg once a week and stepped up every four weeks to their assigned dose of 4 mg, 9 mg or 12 mg, or placebo. Their average starting weight was 112.7 kg (248 lb) with a BMI of 40. The full escalation schedule is in our guide to retatrutide dosage in clinical trials.

The efficacy estimand asks what happens if people take the drug as intended. The treatment-regimen estimand includes everyone, even those who stopped or switched. The second is the more conservative, real-world-leaning number. Neither is a trick, but quoting one without saying which is misleading.

Those milestones are why retatrutide gets compared with bariatric surgery. Nearly half of people on 12 mg lost 30% or more. The flip side: more than a third didn't reach 25%, so the average hides a wide spread.

You'll also see "30% weight loss" online. That comes from a 24-week extension of TRIUMPH-1 in 532 people who started with a BMI of 35 or more and continued to 104 weeks at their maximum tolerated dose. They lost an average of 30.3% on the 12 mg arm. It's a subgroup with higher starting weight, so it can't be applied to everyone in the trial.

Weight loss in the trials was gradual because doses were raised slowly to limit nausea, and most of it came in the first year. In the Phase 2 study, weight had not fully leveled off by 48 weeks, and the longer Phase 3 trials report bigger numbers, which suggests the effect keeps building for well over a year on the higher doses.

Lilly says it plans to submit retatrutide to FDA by the end of the first quarter of 2027, which makes an approval decision realistic in 2027 or 2028. TRIUMPH-5, the direct comparison with tirzepatide, runs to the end of 2026. Our approval watch tracks each step.

Retatrutide's weight-loss results are the strongest of any obesity drug so far: about 25% to 28% on the 12 mg dose over 80 weeks in people with obesity, and around 21% in people with type 2 diabetes. The numbers are averages from controlled trials with slow dose increases and medical supervision. They don't yet tell us about head-to-head performance, muscle, or what happens after stopping.