Retatrutide (retatrutide (LY3437943))
Lilly's triple-agonist next-gen weight loss drug. Strongest results in trials to date.
Retatrutide is Eli Lilly's next-generation triple agonist — activating GLP-1, GIP, AND glucagon receptors. In Phase 2 trials it produced ~24% body weight reduction over 48 weeks, the strongest weight-loss results of any peptide drug to date.
Overview
Retatrutide (LY3437943) is in Phase 3 trials. Lilly anticipates FDA submission in 2026. As a triple agonist, it activates the same receptors as tirzepatide (GLP-1, GIP) plus the glucagon receptor — producing additional metabolic effects on fat oxidation and energy expenditure.
How Retatrutide Works
Triple receptor activation. The GLP-1 + GIP combination provides appetite suppression and insulin potentiation; glucagon receptor activation increases energy expenditure and may directly target visceral fat. The result: stronger weight loss than dual agonists.
Dosing & Schedule
Phase 2 used 1, 4, 8, and 12 mg weekly. The 12 mg dose produced ~24% weight loss. Phase 3 doses still being finalized.
Effectiveness — Trial Data
Phase 2 trial (TRIUMPH-1, 48 weeks): 24.2% weight loss at 12 mg. Phase 3 trials (TRIUMPH-3, TRIUMPH-4) are ongoing through 2026.
Side Effects
GI effects similar to tirzepatide. Glucagon agonism could theoretically raise blood sugar, but glucose-dependent GLP-1 effect appears to dominate. Long-term safety data still being collected.
Cost — How Much Retatrutide Costs in 2026
Not yet on market. Pricing will likely be similar to or above Zepbound at launch.
Who Is Retatrutide For?
Phase 3 enrolling adults with obesity. Once approved, expected indications: chronic weight management, possibly type 2 diabetes and MASH/NASH.
Retatrutide Alternatives
Available now: tirzepatide (closest analog), semaglutide.