Lilly’s Retatrutide Delivers 28.3% Weight Loss but 11.3% Discontinuation
LLY•In the 80-week Phase III TRIUMPH-1 trial, Lilly’s retatrutide delivered up to 28.3% mean weight loss versus 2.2% for placebo and enabled 45.3% of high-dose patients to shed over 30% of body weight. High-dose discontinuation due to adverse events reached 11.3% versus 4.9% with placebo.
1. Trial Design and Endpoints
The 80-week Phase III TRIUMPH-1 trial evaluated retatrutide at 4mg, 9mg and 12mg doses against placebo in obese adults with at least one weight-related comorbidity, meeting primary weight-loss and key secondary endpoints across all dose groups.
2. Efficacy and Cardiovascular Effects
Patients receiving the 12mg dose lost a mean 28.3% of baseline weight versus 2.2% for placebo, with 45.3% achieving over 30% weight loss; medium and low doses saw 37.9% and 15.3% reach that threshold. Retatrutide also produced significant reductions in waist circumference, triglycerides, systolic blood pressure, non-HDL cholesterol and hsCRP, with detailed data pending.
3. Adverse Events and Market Implications
High-dose discontinuation due to adverse events reached 11.3%, compared with 4.9% for placebo, raising concerns that tolerability may confine retatrutide use to patients with the highest BMI. Lilly’s established tirzepatide franchise generated $23bn (Mounjaro) and $13.5bn (Zepbound) in 2025 sales, highlighting competitive challenges for the new agent.
