On 26 June 2023, Eli Lilly reported phase 2 results for retatrutide, an investigational once-weekly injectable that agonises three receptors — GLP-1, GIP and glucagon. The randomised, double-blind, placebo-controlled trial enrolled 338 adults with obesity or overweight without type 2 diabetes, testing 1, 4, 8 and 12 mg subcutaneous doses.
The primary endpoint at 24 weeks showed mean weight reduction of up to 17.5% (about 18.7 kg) at the highest dose. As a secondary endpoint at 48 weeks, the 12 mg group reached a mean reduction of 24.2%, roughly 26.2 kg.
The most common adverse events were gastrointestinal — nausea, vomiting and diarrhoea — consistent with the incretin drug class and generally dose-related. Exploratory endpoints showed improvements in blood pressure, lipids and glycaemic measures.
The results were published simultaneously in the New England Journal of Medicine and presented at the American Diabetes Association's 83rd Scientific Sessions. Phase 3 (the TRIUMPH programme) was subsequently initiated to confirm efficacy and safety at scale.