Researchers reported that the experimental weekly injection retatrutide generated an average 25 percent reduction in body weight after 80 weeks at its highest dose in a large phase 3 trial. The study also documented meaningful decreases in knee‑joint pain and obstructive sleep‑apnea events, suggesting broader health benefits for people with obesity.
Trial design and primary outcomes
The double‑blind, placebo‑controlled trial enrolled 2,339 adults who were classified as obese but did not have diabetes. Participants were randomly assigned to receive weekly injections of either 4 mg, 9 mg, 12 mg of retatrutide, or a placebo. Neither the participants nor the investigators knew which treatment was administered.
Retatrutide is designed to activate three hormonal receptors—GLP‑1, GIP and glucagon—in an effort to curb appetite while potentially increasing energy expenditure. After a meal, these hormones help regulate nutrient processing, blood‑sugar levels and hunger signals.
At the 80‑week mark, average weight loss was 17.6 percent in the 4‑mg group, 23.7 percent in the 9‑mg group, and 25 percent in the 12‑mg group, compared with a 3.9 percent loss in the placebo arm. The calculations accounted for participants who discontinued the drug or began prohibited weight‑management therapies.
Following the initial period, the first participants who completed 80 weeks entered a 24‑week extension. Of the 532 individuals in this extension, those originally on the 12‑mg dose continued at a tolerated dose of 9 mg or 12 mg. Their average weight loss reached 29.9 percent after 104 weeks. Statistical models that adjusted for certain protocol deviations projected a 30.3 percent loss for the same cohort.
Impact on obesity‑related complications
The trial also measured two common conditions linked to obesity. Among 574 participants with knee osteoarthritis, the 12‑mg group experienced a 4.1‑point reduction on a 0‑to‑10 pain scale, versus a 2.5‑point reduction with placebo. In the subset of 243 participants with obstructive sleep apnea, the highest dose cut the average number of apnea events by 32.1 per hour, compared with a 9.6‑event reduction in the placebo group.
Safety profile and study limitations
Gastrointestinal side effects were the most frequently reported adverse events, occurring mainly during dose escalation. Approximately 42 percent of participants receiving the 12‑mg dose reported nausea. Treatment discontinuation due to adverse events affected 11 percent of the highest‑dose group, versus 4.6 percent on placebo. Serious adverse events were recorded in 10.5 percent of the 12‑mg cohort and 5.5 percent of placebo participants; the trial was not designed to determine causality.
The study was funded by Eli Lilly, which also collected and analyzed the data. While the findings demonstrate substantial weight loss and improvements in knee pain and sleep apnea, the trial did not assess cardiovascular safety and did not directly compare retatrutide with existing obesity drugs such as semaglutide or tirzepatide.
Results were published in The New England Journal of Medicine, providing the most extensive clinical evidence to date on retatrutide’s efficacy for obesity and related health issues.
Norman Pearlstine is the Executive Editor and Co-Founder at News Raise. With over two decades of experience across financial journalism, corporate governance, and market analysis, Norman leads the editorial direction and ensures strict adherence to journalistic accuracy and ethics.
