Retatrutide TRIUMPH-1 Phase 2: 24% mean weight loss at 48 weeks with triple-agonist mechanism

TRIUMPH-1 (Jastreboff et al., NEJM June 2023; PMID 37366315) reported the largest Phase 2 weight-loss signal of any GLP-1 class drug to date. 338 adults with obesity received retatrutide at one of four doses or placebo for 48 weeks.

Headline numbers

Mean weight loss at 48 weeks, 12 mg arm: −24.2%. Placebo arm: −2.1%. Lower doses (4 mg, 8 mg) produced 18-22% mean loss. The dose-response was linear across the studied range, suggesting higher doses might extend the loss curve further.

Mechanism — triple agonist

Retatrutide activates GLP-1, GIP, and glucagon receptors. The glucagon component is the differentiator: glucagon agonism increases hepatic energy expenditure and lipid oxidation, complementing the appetite-suppression of the GLP-1/GIP combination. The risk side: glucagon can complicate glycemic control, and TRIUMPH-1 reported some hyperglycemia signal at higher doses in non-diabetic subjects.

Phase 3 TRIUMPH program

Three Phase 3 trials launched in late 2023: TRIUMPH-3 (cardiovascular outcomes), TRIUMPH-4 (chronic weight management), and TRIUMPH-OUTCOMES. Primary readouts expected Q3 2026 - 2027. The 12 mg dose is the lead candidate for the chronic-weight-management indication.