TRIUMPH-1 Results: 28.3% Average Weight Loss at 80 Weeks (May 21, 2026)
TRIUMPH-1 results, May 21, 2026: retatrutide 12 mg gave 28.3% average weight loss at 80 weeks, or 25.0% counting everyone. Doses, side effects and what's next.
Event date Last verified Primary source Eli Lilly and Company (PR Newswire)
The TRIUMPH-1 results, which Lilly released on May 21, 2026, showed retatrutide 12 mg taking off 28.3% of body weight on average after 80 weeks, against 2.2% on placebo. That's the efficacy estimand, as if everyone stayed on treatment; counting everyone randomized, it was 25.0% against 3.9%. The primary source is Lilly's May 21 release, and TRIUMPH-1 is the trial behind most retatrutide weight headlines.
Key takeaways
- Lilly reported TRIUMPH-1, its main obesity trial, on May 21, 2026: 2,339 adults without diabetes on 4, 9 or 12 mg or placebo for 80 weeks.
- Weight fell 19.0%, 25.9% and 28.3% on the three doses against 2.2% on placebo, using the efficacy estimand.
- About 6 in 10 people on 12 mg (62.5%) lost a quarter or more of their body weight.
- In a 104-week extension, people who started at a BMI of 35 or more lost up to 30.3% on average.
This page is the dated record of the topline. The full trial, including its knee pain and sleep apnea groups, is on the TRIUMPH-1 page.
What Lilly reported on May 21
TRIUMPH-1 randomized 2,339 adults with obesity, or overweight plus at least one weight-related condition, and no diabetes, 1:1:1:1 to 4 mg, 9 mg, 12 mg or placebo once a week. It ran 80 weeks. Everyone started at 2 mg and stepped up every 4 weeks to their target dose. The trial is a master protocol with two basket groups inside it, for knee osteoarthritis and for sleep apnea, which Lilly presented in June.
The TRIUMPH-1 results by dose
Average weight lost by dose in TRIUMPH-1
80 weeks, 2,339 adults with obesity or overweight (efficacy estimand)
From a starting weight of 112.7 kg (248.5 lb), 12 mg took off 31.9 kg (70.3 lb) on average. Waists shrank by 24.1 cm (9.5 in) on 12 mg against 3.6 cm (1.4 in) on placebo. The share of people reaching big milestones, using the efficacy estimand:
| Lost at least | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| 25% of body weight | 27.8% | 52.9% | 62.5% | 2.2% |
| 30% | 15.3% | 37.9% | 45.3% | 0.5% |
| 35% | 5.9% | 20.8% | 27.2% | 0.3% |
On 12 mg, 65.3% ended with a BMI under 30. Counting everyone randomized (the treatment-regimen estimand), the averages were 17.6%, 23.7% and 25.0% against 3.9%.
Side effects Lilly reported
Nausea hit 28.6%, 38.4% and 42.4% of people on 4, 9 and 12 mg against 14.8% on placebo, and vomiting 10.6%, 22.8% and 25.3% against 4.8%. Burning or oversensitive skin (dysesthesia) showed up in 5.1%, 12.3% and 12.5% against 0.9%, mostly mild to moderate. Stopping because of side effects ran 4.1%, 6.9% and 11.3%, against 4.9% on placebo, so 4 mg came in below placebo.
What the 104-week extension added
Lilly also reported an extension. The first 532 people who finished 80 weeks on the drug with a starting BMI of 35 or more stayed on retatrutide for 24 more weeks, escalated blind to the highest dose they could tolerate, 9 or 12 mg, including people who'd been on placebo. At 104 weeks, from 121.7 kg (268.3 lb), the original 12 mg group had lost 30.3% on the efficacy estimand and 29.9% on the treatment-regimen estimand. Lilly released no safety or discontinuation numbers for the extension.
Our read: 28.3% is the figure you'll see everywhere, and it's a fair estimate of what happens if everyone stays on treatment. If you're setting your own expectations, 25.0% is the more cautious number from the same trial.
What came next
Lilly presented TRIUMPH-1 in detail at the ADA meeting on June 6, and NEJM published it on September 29, 2026, leading with the 25.0% figure; the September 29 news page covers the paper. The retatrutide results page puts TRIUMPH-1 alongside the other trials, and retatrutide vs tirzepatide covers what can be compared before TRIUMPH-5, the head-to-head trial, reports.
No approved version exists yet, and anything listed as retatrutide for sale online isn't the drug TRIUMPH-1 tested.
Frequently asked questions
What were the TRIUMPH-1 results?
After 80 weeks, average weight loss was 19.0% on 4 mg, 25.9% on 9 mg and 28.3% on 12 mg, against 2.2% on placebo, using Lilly's efficacy estimand. Counting everyone randomized, the figures were 17.6%, 23.7% and 25.0% against 3.9%.
How many people lost 30% or more of their weight?
On 12 mg, 45.3% lost 30% or more and 27.2% lost 35% or more, against 0.5% and 0.3% on placebo (efficacy estimand).
What side effects did people have in TRIUMPH-1?
Mostly stomach and gut effects. On 12 mg, 42.4% had nausea against 14.8% on placebo, and 25.3% vomited against 4.8%. Burning or oversensitive skin (dysesthesia) affected 12.5% against 0.9%. On 12 mg, 11.3% stopped because of side effects.
Did weight keep falling after 80 weeks?
In the extension, 532 people with a starting BMI of 35 or more stayed on retatrutide for 24 more weeks at up to 9 or 12 mg. At 104 weeks, those who started on 12 mg had lost 30.3% on average (efficacy estimand).
Sources
- Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial (TRIUMPH-1 topline). Eli Lilly and Company (PR Newswire), 2026. prnewswire.com
- Jastreboff AM et al., Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity (TRIUMPH-1). The New England Journal of Medicine, 2026. doi.org
- A Study of Retatrutide (LY3437943) Compared to Tirzepatide (LY3298176) in Adults Who Have Obesity (TRIUMPH-5), NCT06662383. ClinicalTrials.gov, U.S. National Library of Medicine, 2026. clinicaltrials.gov
Dr. Juan Pablo Frías, MD
Physician-Scientist & Clinical Trialist • Endocrinology, Diabetes & Metabolism
Dr. Frías earned his M.D. from Vanderbilt University School of Medicine and completed his endocrinology fellowship at UC San Diego. A principal investigator on landmark incretin trials (including retatrutide, tirzepatide and semaglutide), he reviews all guides on Retatrutide360 for clinical accuracy, dosing safety and evidence fidelity.
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