Experimental Obesity Drug Retatrutide Delivers 25% Weight Loss in Phase 3 Trial

NEW HAVEN, Conn., Oct. 3 (TodayViralUSA) — An experimental weekly injection that targets three metabolic hormone pathways produced average weight loss of about 25 percent after 80 weeks at its highest dose in a large phase 3 trial, researchers reported in The New England Journal of Medicine.

The study, led by obesity researcher Ania Jastreboff of Yale University and funded by manufacturer Eli Lilly, enrolled 2,339 adults with obesity but without diabetes. Participants were randomly assigned to weekly retatrutide doses of 4, 9 or 12 milligrams, or to placebo, in a double-blind design.

After 80 weeks, average weight reductions — in analyses that accounted for people who stopped treatment or started other weight-management therapies — reached 17.6 percent on 4 milligrams, 23.7 percent on 9 milligrams and 25 percent on 12 milligrams, compared with 3.9 percent on placebo.

Knee pain, sleep apnea and longer follow-up

Retatrutide activates receptors for GLP-1, GIP and glucagon, a combination developers hope will curb appetite while increasing energy expenditure. In a subgroup of 574 participants with knee osteoarthritis, pain scores on a 0–10 scale fell by an average of 4.1 points at the highest dose versus 2.5 points with placebo. Among 243 participants with obstructive sleep apnea, breathing interruptions fell by an average of 32.1 events per hour on the top dose, compared with 9.6 on placebo.

A smaller extension that followed 532 eligible participants for a total of about two years found average weight loss approaching 30 percent among those continuing near the highest dose. Those figures come from people who entered the extension and use differing statistical assumptions; they do not represent a full two-year placebo-controlled comparison for the entire original cohort.

Gastrointestinal side effects were common, especially during dose increases. About 42 percent of the highest-dose group reported nausea. Roughly 11 percent stopped treatment because of adverse events, versus 4.6 percent on placebo. Serious adverse events were recorded in 10.5 percent of the high-dose group and 5.5 percent on placebo; recording an event does not prove the drug caused it.

The trial was not designed to prove cardiovascular safety and did not directly compare retatrutide with marketed drugs such as semaglutide or tirzepatide. Retatrutide remains experimental and is not approved for routine clinical use. Lilly collected and analyzed the trial data. Outside clinicians will watch forthcoming regulatory filings and longer safety studies before the drug’s place among obesity therapies becomes clear.