TRIUMPH-1: retatrutide hits 28.3% weight loss at 80 weeks

On 21 May 2026 Eli Lilly reported the topline result from TRIUMPH-1, the first general-obesity Phase 3 trial of retatrutide, the triple GLP-1 / GIP / glucagon receptor agonist. In 2,339 adults with obesity or overweight and at least one weight-related comorbidity but without diabetes, retatrutide 12 mg produced a mean 28.3% body-weight reduction at 80 weeks versus 2.2% on placebo^[1].

The numbers

The 9 mg dose produced 25.9% mean weight loss; the 4 mg dose 19.0%. Placebo participants lost 2.2%. The 28.3% figure on the top dose is the largest mean weight loss reported in any Phase 3 obesity trial of an incretin-class medicine to date, exceeding the SURMOUNT-1 tirzepatide 15 mg result of 20.9% at 72 weeks and the STEP-1 semaglutide 2.4 mg result of 14.9% at 68 weeks.

Safety signals to read

The dominant adverse-event pattern was gastrointestinal, dose-dependent and consistent with the broader class. Nausea ran 28.6% to 42.4% across the active arms; diarrhoea 25.2% to 34.1%; vomiting 10.6% to 25.3%; constipation 23.8% to 26.1%. Trial discontinuation for adverse events ranged from 4.1% on 4 mg to 11.3% on 12 mg, against 4.9% on placebo. A dose-dependent dysesthesia signal (skin sensitivity, 5.1% to 12.5% versus 0.9% on placebo) is new and worth following.

What this is not

TRIUMPH-1 is a topline release, not a peer-reviewed publication. The full results have not yet appeared in the New England Journal of Medicine or the Lancet, and the per-subgroup body-composition and cardiovascular-marker data are still pending. The head-to-head trial against tirzepatide is TRIUMPH-5, which has not yet read out. And the long-horizon cardiovascular outcomes data is TRIUMPH-Outcomes, a 10,000-participant trial whose primary completion is February 2029.

Where retatrutide sits today

Investigational. Not approved by the FDA, the EMA, the MHRA, or any national agency we track. Per-country status is on the retatrutide regulation pages. The FDA has, since September 2025, sent a coordinated wave of warning letters to compounding pharmacies selling unauthorised retatrutide; the agency's position is that retatrutide "cannot be used in compounding under federal law."

What to watch next

Peer-reviewed publication of the full TRIUMPH-1 dataset; the TRIUMPH-5 head-to-head against tirzepatide; and TRIUMPH-Outcomes for the hard-outcomes question. The 28.3% headline is striking; the durability question (what happens at year three, year five) is what will decide whether retatrutide becomes the standard.