Eli Lilly and Co.’s newest experimental weight-loss shot helped participants in a clinical trial lose more weight than any other obesity medication on the market, the company announced last week.
The Indianapolis-based drugmaker said some participants in the Phase 3 trial lost 28% of their body weight after 80 weeks. That is a level of weight loss similar to what patients experience after bariatric surgery, which is typically the only effective treatment for people with severe obesity.
Retatrutide is a once-weekly injectable drug designed to target three hormone receptors that control appetite and metabolism: GLP-1, GIP and glucagon. Lilly’s Zepbound targets GLP-1 and GIP, while Denmark-based Novo Nordisk’s Wegovy affects GIP. Neither targets glucagon. Lilly also produces the once-daily weight-loss pill Foundayo, which targets the GLP-1 receptor.
Kenneth Custer, president of Lilly Cardiometabolic Health, said the trial highlights the importance of people having options for obesity medications.
“Together with Zepbound and Foundayo, retatrutide could build on Lilly’s commitment to match treatments to the needs and preferences of patients,” Custer said in a press release.
The results of the Phase 3 clinical trial indicate retatrutide could be the most powerful obesity medication yet.
In the study of 2,339 patients, people who took 12 milligrams of retatrutide lost an average of 70.3 pounds, or 28% of their body weight, after 80 weeks, according to Lilly. Nearly half of the patients in that group lost an average of 30% of their body weight. Additionally, people who took a 4 mg dose lost an average of 47.2 pounds and participants who took a 9 mg dose lost an average of 64.4 pounds.
Participants in an extension study who had a body mass index of 35 or higher lost an average of 85 pounds, or 30.3% of body weight, after 104 weeks.
Lilly reported that 11% participants in the retatrutide trial stopped taking the medication because they felt they were losing too much weight.
Comparatively, patients who use Wegovy or Zepbound can lose up to about 20% of their body weight.
Dr. Ania Jastreboff, a professor at Yale University School of Medicine who led the trial, said every dose of retatrutide “resulted in clinically meaningful weight reduction for nearly all participants.” She said people treated with retatrutide also showed improvement in their cardiometabolic health measures.
“Obesity is a chronic disease, and people living with obesity deserve treatment options that match the complex biology of their neurometabolic disease,” Jastreboff said in a press release. “For patients I see in clinic, retatrutide may potentially be a highly impactful future tool to treat their obesity and transform their health trajectory.”
About 11% of participants taking the highest dose of retatrutide discontinued treatment due to side effects. The most common side effects people reported in the trial were gastrointestinal issues, such as nausea, diarrhea, vomiting and constipation.
In 2024, Lilly sued the U.S. Food and Drug Administration after the agency rejected Lilly’s request to designate retatrutide as a biological product and instead classified it as a drug. The lawsuit is still pending. The difference for Lilly is that if it can convince the court to rule that retatrutide is a biological product, the treatment could get 12 years of market exclusivity instead of five years given to drugs under the law.
Lilly has not yet applied for regulatory approval of retatrutide. Additional results from the trial will be presented at the American Diabetes Association Scientific Sessions from June 5-8 in New Orleans.
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