Eli Lilly reported on Thursday, May 21, 2026, that its experimental obesity medication retatrutide delivered unprecedented weight loss results in clinical trials. According to the latest company announcement, patients taking the highest weekly dose lost an average of 28% of their body weight, equivalent to approximately 70 pounds, over the 80-week study period. Most significantly, a smaller group of patients with severe obesity who continued treatment for up to 104 weeks lost an average of 85 pounds, representing the largest weight loss ever seen in any medication trial. As reported by Reuters, this late-stage trial involved individuals with obesity but not diabetes who received the maximum dose of 12 milligrams of retatrutide. Over 45% of participants lost at least 30% of their body weight over the 80-week study period, with the company claiming this level of efficacy rivals bariatric surgery.
In the rapidly expanding obesity treatment market where Lilly competes with Novo Nordisk, the record-breaking results position retatrutide as potentially the most powerful weight-loss drug in the booming obesity treatment market. As reported by Reuters, Lilly's stock increased 1% during morning trading, while Novo's shares were down 0.7% by 1330 GMT. The company's current licensed injection, Zepbound, has demonstrated weight loss of approximately 15% to 20% in various trials, while Lilly's oral obesity pill candidate has produced weight loss of approximately 11%. According to Citi analyst Geoff Meacham, "This is the figure that most impresses us, given it confers a level of efficacy previously unheard of and is substantially better than even Lilly's own tirzepatide." Dr. Susan Spratt from Duke Health noted that "this is the largest weight loss I've ever seen in any medication trial," calling it "huge."
Retatrutide distinguishes itself as a triple agonist medication, mimicking not only GLP-1 but also GIP and glucagon hormones, compared to Lilly's Zepbound, which is a double agonist mimicking GLP-1 and GIP. The latest results are based on a phase 3 trial of approximately 2,300 patients with obesity or overweight conditions, as reported by Lilly. The trial ran for 80 weeks for most participants, with a smaller group continuing treatment for up to 104 weeks. By comparison, in trials, patients taking the highest dose of Zepbound lost around 21% of their body weight over 72 weeks and patients taking the highest dose of Wegovy lost around 15% after 68 weeks. The drug company did not publish the full results in a medical journal, though the results are consistent with Wall Street estimates.
Analysts had previously voiced concerns regarding the drug's adverse effects after data from prior trials revealed that individuals had developed dysesthesia, an uncommon, unpleasant skin sensation. According to Reuters, the most recent data seemed to allay some of those concerns, with 12.5% of patients on the 12 mg dose experiencing dysesthesia, compared to 20.9% of patients on the highest dose in the December study result. Nausea, constipation and diarrhea were among the side effects of retatrutide, which are often seen with GLP-1 drugs. Lilly also reported that compared with placebo, patients taking retatrutide had more reports of unusual or uncomfortable skin sensations and urinary tract infections. The rate of people dropping out of the trial was higher than what was seen for Zepbound but similar to rates seen with Wegovy, as noted by Lilly.
According to Lilly, retatrutide is in the same class of medications as Wegovy and Zepbound, which mimic a hormone called GLP-1, but its triple agonist mechanism sets it apart. The company announced that the phase 3 trial results allow the company to seek regulatory approval and potentially launch the next-generation drug next year. Dr. Shauna Levy from Tulane Weight Loss Center noted that "there's about 10% of patients that don't respond to GLP-1s," making retatrutide potentially very useful for patients who are GLP-1 non-responders. If approved, the drug could be ideal for patients who do not lose weight on the current generation of GLP-1s. The medication's side effect profile was generally comparable to those of other GLP-1 medications, as noted by Lilly, with the company planning to introduce the medication next year after regulatory approval.
