In a phase 3 randomized trial of 2,339 adults with obesity (no diabetes), weekly retatrutide produced dose-dependent weight loss: 25.0% average at 12 mg after 80 weeks and nearly 30% in a subgroup at 104 weeks. The treatment also reduced knee pain and obstructive sleep apnea events more than placebo. Gastrointestinal side effects were common and led to higher discontinuation rates; the study was not designed to assess cardiovascular safety and did not directly compare retatrutide with approved drugs.
Retatrutide Cuts Weight By 25% in Phase 3 Trial — Nearly 30% After Two Years, With Improved Knee Pain and Sleep Apnea
(rostislavsedlacek/Canva)
For many people with obesity, everyday activities — from climbing stairs to sleeping through the night — are affected by more than just body weight. A large phase 3 trial of the investigational weekly injection retatrutide found substantial, dose-dependent weight loss and improvements in two common obesity-related complications: knee pain and obstructive sleep apnea.
Study Design
The randomized, double-blind phase 3 trial led by Ania Jastreboff at Yale enrolled 2,339 adults with obesity who did not have diabetes. Participants received once-weekly injections of retatrutide at 4 mg, 9 mg, or 12 mg, or a matching placebo. Neither participants nor investigators knew treatment assignments.
Primary Weight-Loss Results
After 80 weeks, mean weight loss showed a clear dose response: 17.6% (4 mg), 23.7% (9 mg) and 25.0% (12 mg), versus 3.9% for placebo. These figures account for participants who discontinued treatment or started prohibited weight-management therapies, and reflect average outcomes — individual results varied.
Longer-Term Extension
An early completer extension enrolled 532 participants for an additional 24 weeks. Those randomized originally to 12 mg who continued at their maximum tolerated dose (9 or 12 mg) reached an average weight loss of 29.9% after 104 weeks. A sensitivity analysis using an alternative statistical approach estimated roughly 30.3% for this subgroup; methodological differences explain variations between reported estimates. Participants who received placebo in the main trial were switched to active drug during the extension, so the extension is not a two-year randomized drug-versus-placebo comparison.
Other Clinical Outcomes
Among 574 participants with knee osteoarthritis, pain scores fell more with retatrutide: an average decrease of 4.1 points on a 0–10 scale with 12 mg versus 2.5 points with placebo (analysis accounting for treatment discontinuation and related events). In 243 participants with obstructive sleep apnea, the highest dose reduced respiratory events by an average of 32.1 events/hour, compared with 9.6 events/hour for placebo.
Safety and Tolerability
Gastrointestinal adverse effects were the most frequent side effects and were typically mild to moderate, occurring mainly around dose increases. About 42% of participants on the highest dose reported nausea. Adverse events led roughly 11% of the highest-dose group to discontinue treatment versus 4.6% in the placebo group. Serious adverse events were reported in 10.5% of participants on the highest dose and 5.5% of those on placebo; recording a serious event does not establish causation by the drug.
Limitations and Context
The trial was not designed to establish cardiovascular safety and did not directly compare retatrutide with currently approved agents such as semaglutide or tirzepatide. The manufacturer, Eli Lilly, funded the study and collected and analyzed the data. The full results are published in The New England Journal of Medicine, allowing independent scientific scrutiny as development proceeds.
Bottom line: Retatrutide produced substantial, dose-dependent weight loss and measurable improvements in knee pain and sleep apnea compared with placebo, but gastrointestinal side effects and higher rates of discontinuation highlight tolerability concerns. Further research is needed to define long-term safety, cardiovascular outcomes, and direct comparisons with existing therapies.
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