Retatrutide (Triple Agonist, Investigational)

Retatrutide is Eli Lilly's investigational triple receptor agonist, simultaneously activating GLP-1, GIP, and glucagon receptors — a pharmacological combination with no approved precedent. By adding glucagon receptor agonism to the dual GIP/GLP-1 profile of tirzepatide, retatrutide targets a third metabolic axis: energy expenditure. Glucagon receptor activation increases thermogenesis and fat oxidation in the liver and adipose tissue, providing a mechanism for weight loss that goes beyond appetite suppression alone. The Phase 2 trial published in 2023 showed up to 24% weight loss at 48 weeks in adults without diabetes at the 12 mg weekly dose — results that electrified the obesity medicine field. Then the Phase 3 program delivered results that were even more remarkable. TRIUMPH-4, reported in December 2025, showed a mean body-weight reduction of 28.7% at 68 weeks in the 12 mg group. Most strikingly, TRIUMPH-1, the pivotal obesity trial with its topline data announced in May 2026, reported up to 30.3% average weight loss at the highest dose — the single greatest weight-loss result ever recorded in a randomized Phase 3 clinical trial. At 12 mg over 96 weeks, participants had lost an average of approximately 70-71 pounds. Additional TRIUMPH-4 findings included a 75.8% reduction in osteoarthritis pain scores, approximately 20% reduction in LDL cholesterol, and a 72% reversal rate of prediabetes to normoglycemia. An NDA filing with the FDA is anticipated in late 2026, with approval expected in late 2027. Seven additional Phase 3 trials are reporting throughout 2026 across obesity subtypes, type 2 diabetes, and cardiovascular disease. Retatrutide does not yet have a commercial brand name, a list price, or an approved indication — but given the Phase 3 data, it represents the most anticipated drug in obesity medicine since Wegovy's 2021 approval.