Lilly retatrutide shows 28.3% weight loss

Eli Lilly said on May 21 that its experimental obesity drug retatrutide delivered up to 28.3% mean weight loss in a Phase 3 trial, extending the company’s push beyond Zepbound into a new class of weekly medicines. The result came from TRIUMPH-1, a late-stage study in adults with obesity or overweight and at least one weight-related condition, but without diabetes, according to Lilly’s statement. The company said the top-line readout covered 80 weeks of treatment and met the trial’s primary endpoint. Lilly did not announce a regulatory filing date in the release. ### Where did the 28.3% figure come from? TRIUMPH-1 tested retatrutide as a once-weekly injection in adults with obesity or overweight plus at least one weight-related comorbidity and no diabetes, Lilly said. The 28.3% figure was the average body-weight reduction at 80 weeks in the highest-dose group among participants who stayed on treatment, compared with 2.2% for placebo on the same measure, according to Lilly and CNBC’s report on the company’s announcement. (investor.lilly.com) Healio reported that the 80-week top-line results showed weight loss of up to 28.3% with the triple receptor agonist, describing the readout as part of Lilly’s Phase 3 obesity program. LifeSciVoice separately reported the same top-line number on May 22, citing Lilly’s announcement. (investor.lilly.com) ### What kind of drug is retatrutide? Lilly described retatrutide as an investigational first-in-class GIP, GLP-1 and glucagon triple hormone receptor agonist. That distinguishes it from Lilly’s marketed obesity drug Zepbound, tirzepatide, which targets GIP and GLP-1 but not glucagon. (healio.com) Science Media Centre said experts commenting on the topline release noted that retatrutide’s three-hormone approach is different from currently approved obesity medicines, while also stressing that the May 21 disclosure was based on a company announcement rather than a full published paper. (investor.lilly.com) ### How does this compare with Lilly’s earlier retatrutide data? Lilly has already reported other late-stage retatrutide results in adjacent settings. In December 2025, the company said retatrutide produced up to 28.7% average weight loss at 68 weeks in a Phase 3 trial involving patients with obesity and knee osteoarthritis. In March 2026, Lilly said a separate Phase 3 diabetes study showed up to 16.8% weight loss at 40 weeks with the 12 mg dose. (sciencemediacentre.org) AJMC reported that the new TRIUMPH-1 topline announcement also referenced a 104-week figure of 30.3% average weight loss, though Lilly’s May 21 release highlighted the 80-week 28.3% result. Reuters could not independently verify additional subgroup details from the company statement because full trial data were not yet public. (investor.lilly.com) ### What did Lilly say about safety? Lilly said the overall safety profile in TRIUMPH-1 was consistent with the incretin class, with gastrointestinal side effects the most commonly reported adverse events. AJMC reported that discontinuation rates rose with dose, while Science Media Centre said outside experts cautioned that full safety interpretation will depend on peer-reviewed data and conference presentation details. (ajmc.com) ### What happens next? Lilly said detailed TRIUMPH-1 results will be presented at a medical meeting and published in a peer-reviewed journal. The company is also studying retatrutide in several other Phase 3 trials, including obesity with cardiovascular disease and weight-loss maintenance, according to Lilly trial listings. As of May 23, Lilly had not publicly announced a filing date with the U.S. Food and Drug Administration for retatrutide based on TRIUMPH-1. (ajmc.com) (investor.lilly.com)