TRIUMPH-1 results: 25% average weight loss at 80 weeks

On 21 May 2026 Lilly announced topline results from TRIUMPH-1, the largest retatrutide trial so far and the one most headlines quote. Across 2,339 adults with obesity or overweight and no diabetes, the highest dose produced an average 25.0% weight loss at 80 weeks, against 3.9% on placebo.^[1]

What was announced

TRIUMPH-1 is the trial the whole retatrutide story rests on: the biggest, the longest, and the one that will anchor any licence application. Lilly gave both ways of counting. On the treatment-regimen estimand, which includes everyone randomised whether or not they stayed on the drug, the three arms lost 17.6%, 23.7% and 25.0% and placebo lost 3.9%. On the efficacy estimand, which counts people while they stayed on treatment, the figures were 19.0%, 25.9% and 28.3% versus 2.2%.^[1]

Large losses were common on the higher doses. In the 12 mg arm, 62.5% of people lost at least a quarter of their body weight and 45.3% lost at least 30%, against 2.2% and 0.5% on placebo. Waist size fell by 9.5 inches versus 1.4 inches. Cholesterol, triglycerides, blood pressure and the inflammation marker hs-CRP all improved.^[1]

A sub-group of 532 people who started with a BMI of 35 or more continued to 104 weeks. On the 12 mg arm they reached an average 30.3% loss (efficacy estimand; 29.9% on the treatment-regimen estimand). People switched from placebo to the drug had lost 19.2% by week 104.^[1] The full breakdown is on the TRIUMPH-1 page.

Side effects and drop-outs

Nausea was reported by 28.6%, 38.4% and 42.4% of the three arms, against 14.8% on placebo. Diarrhoea, constipation and vomiting followed the same dose pattern. Dysesthesia, the altered skin sensation first seen in TRIUMPH-4, affected 5.1%, 12.3% and 12.5% versus 0.9% on placebo.^[1]

Stopping because of side effects rose with dose: 4.1%, 6.9% and 11.3%, against 4.9% on placebo. The lowest dose had a drop-out rate below placebo; the highest dose lost roughly one person in nine. See discontinuation rates.

The release did not report heart-rate or rhythm data, which matters because a dose-related rise in heart rate was seen in Phase 2.^[2] That will come with the peer-reviewed paper.

What is new versus what we knew

TRIUMPH-4 had shown 23.7% (treatment-regimen) in 445 heavy people with knee pain. TRIUMPH-1 showed a near-identical 25.0% in a much larger, broader group, over 80 weeks, and added a two-year figure above 30% in the heaviest participants. The dysesthesia rate was lower than in TRIUMPH-4 (12.5% versus 20.9% at the top dose), and so was the drop-out rate.

What it does not mean

• "30% weight loss" is not the average result. It is the two-year figure in a self-selected sub-group of the heaviest participants who stayed on the top dose. The 80-week average across everyone randomised to that dose was 25.0%.
• The figures describe the trial product, at doses stepped up by doctors, in monitored people. They say nothing about a vial sold online.
• The drug is still investigational. No regulator had received an application at the time of the announcement.

The same month in the UK

Eight days after the announcement, on 29 May 2026, the MHRA arrested two people at a country estate near Northampton and seized about 12,000 doses of unlicensed weight-loss medicines, including retatrutide and tirzepatide. GOV.UK called it the agency's largest ever seizure of unlicensed weight-loss medicines.^[3] It was the third UK site in seven months, after Northampton and Lincolnshire. The contrast is the whole story: the trial numbers come from one product; the seizures are of something else entirely.