Eli Lilly's Retatrutide Shows 28 Percent Weight Loss in Phase 3 Trial, Rivaling Bariatric Surgery

Eli Lilly announced positive results from the Phase 3 TRIUMPH-1 trial for its investigational weight-loss drug retatrutide in May 2026. Participants on the highest dose (12 mg) lost an average of 28.3 percent of their body weight over 80 weeks, compared to 2.2 percent in the placebo group.

The trial enrolled approximately 2,500 adults with obesity or overweight and at least one weight-related health condition, excluding diabetes. A 9 mg dose resulted in 25.9 percent average weight loss, while a 4 mg dose resulted in 19 percent weight loss.

About 45 percent of participants on the 12 mg dose achieved 30 percent or more weight loss, a threshold previously associated with bariatric surgery. About 65 percent of those on the highest dose reached a BMI below 30 by 80 weeks.

In a pre-specified extension for participants with a baseline BMI of 35 or higher, those who continued on the 12 mg dose for 104 weeks achieved an average weight loss of 30.3 percent, or about 85 pounds.

Retatrutide is a triple agonist, meaning it activates three gut hormone receptors: GLP-1, which regulates appetite and slows gastric emptying; GIP, which enhances insulin secretion; and glucagon, which increases energy expenditure and fat oxidation. This three-pronged approach is designed to be more potent than existing dual agonists like tirzepatide or single-incretin therapies like semaglutide.

Common side effects included nausea (42.4 percent at the 12 mg dose), diarrhea (32 percent), constipation (26.1 percent), and vomiting (25.3 percent). The discontinuation rate due to adverse events was 11.3 percent for the 12 mg dose.

Eli Lilly is expected to submit a New Drug Application to the FDA in late 2026. Analysts estimate potential FDA approval in late 2027, with a commercial launch estimated for early 2028.