Eli Lilly and Company on Wednesday announced positive Phase 3 trial results for its experimental obesity drug retatrutide, with patients losing up to 30% of their body weight over two years of treatment.

Retatrutide belongs to a new class of obesity therapies that target three hormones, GIP (glucose-dependent insulinotropic polypeptide), GLP-1 (glucagon-like peptide-1) and glucagon, which help regulate appetite, insulin secretion and energy use in the body.

In the TRIUMPH-1 study, patients receiving the highest 12 mg dose of retatrutide lost an average of 31.9 kg, or 28.3% of their body weight, over 80 weeks. In an extension study involving patients with severe obesity, average weight loss reached 38.5 kg, or 30.3%, over 104 weeks.  

The results strengthen Lilly’s obesity pipeline beyond Zepbound, its already approved obesity treatment. While Zepbound targets GIP and GLP-1 receptors, retatrutide also acts on glucagon receptors, a mechanism that researchers believe may help deliver greater weight reduction.

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The obesity drug market is currently led by Wegovy from Novo Nordisk and Zepbound from Lilly.

According to Lilly, 45.3% of participants on the 12 mg dose achieved at least 30% weight loss, while 65.3% moved below the obesity threshold of BMI 30 after 80 weeks of treatment.  

The trial enrolled 2,339 adults with obesity or overweight and at least one weight-related health condition, excluding diabetes patients. Participants were randomised to receive 4 mg, 9 mg or 12 mg doses of retatrutide or placebo.  

Lilly said the therapy also improved cardiometabolic indicators including waist circumference, triglycerides, blood pressure and inflammatory markers.  

“Obesity is a chronic disease, and people living with obesity deserve treatment options that match the complex biology of their neurometabolic disease,” said Ania Jastreboff, lead investigator of the study.

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The most commonly reported side effects included nausea, diarrhoea, constipation and vomiting. Lilly said these were generally consistent with existing incretin-based obesity medicines. Discontinuation due to adverse events was 11.3% in the 12 mg group compared with 4.9% for placebo.  

Detailed findings from the study will be presented at the annual meeting of the American Diabetes Association next month. Lilly is also studying retatrutide in obesity linked to diabetes, cardiovascular disease, sleep apnea and fatty liver disease.  

Published on: May 21, 2026 8:28 PM IST