Eli Lilly and Company (NYSE: LLY) reported positive topline results from two additional Phase III trials of retatrutide, pushing the investigational triple hormone agonist closer to a regulatory filing. Lilly now has five positive Phase III studies backing retatrutide, a molecule it believes can outperform its own market-leading tirzepatide franchise. The US giant also set a concrete timeline for regulatory submission, indicating that the aim is to file a Biologics License Application to the US FDA in the first quarter of 2027.
The newly reported studies, TRIUMPH-2 and TRIUMPH-3, targeted populations that have historically been harder to treat with weight-loss drugs: people with type 2 diabetes and people with severe obesity complicated by established cardiovascular disease. In TRIUMPH-2, which enrolled 1,152 adults with type 2 diabetes and obesity or overweight, participants on the highest dose of retatrutide lost an average of 49.6 lbs (20.8%) of body weight at 80 weeks, alongside an A1C reduction of up to 1.6 percentage points. In TRIUMPH-3, which enrolled 1,949 adults with severe obesity and cardiovascular disease, the top dose produced average weight loss of 55.8 lbs (22.6%) over the same period.
Weight loss in patients with type 2 diabetes typically lags behind that seen in non-diabetic populations, a consequence of insulin resistance and compensatory metabolic changes. The roughly 20% reduction observed in TRIUMPH-2 is therefore notable in context, even though it falls short of the 28.3% mean loss retatrutide produced in the non-diabetic TRIUMPH-1 population reported earlier this year.
TRIUMPH-3 also included a prespecified cardiovascular safety analysis that revealed no new safety concerns. Although event numbers were low and the trial was not powered for cardiovascular outcomes, retatrutide also improved multiple cardiometabolic biomarkers including triglycerides, non-HDL cholesterol and hsCRP.
Retatrutide works by simultaneously activating three separate receptors — GIP, GLP-1, and glucagon — a mechanism distinct from approved GLP-1 receptor agonists and from Lilly's own dual GIP/GLP-1 agonist tirzepatide. The added glucagon agonism is intended to boost energy expenditure and lipid oxidation beyond what appetite suppression alone can achieve, which is the leading hypothesis for why retatrutide has consistently produced larger weight reductions than its single- and dual-mechanism predecessors across its Phase III program.
Gastrointestinal adverse events — nausea, diarrhea, constipation, vomiting — occurred at higher rates than placebo across both trials and scaled with dose, consistent with the broader incretin drug class. More distinctive was dysesthesia, a sensory disturbance reported in up to 8% of retatrutide-treated patients in TRIUMPH-2 and 6.4% in TRIUMPH-3, compared with under 1.3% on placebo. Lilly said these events were generally mild and self-resolving. However, dysesthesia is not a safety signal associated with approved GLP-1 or dual GIP/GLP-1 agonists, and treatment discontinuations due to adverse events reached 13.5%.