Eli Lilly has reported phase 3 trial results for retatrutide, an experimental once-weekly injectable weight loss drug that produced substantial reductions in body weight among adults with obesity. The company said the TRIUMPH-1 study met its primary and key secondary goals across all tested doses.
Retatrutide is designed to act on three hormone receptors: glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon. Existing medicines such as semaglutide products primarily target GLP-1. Lilly and outside specialists described the triple-receptor approach as a possible next step in obesity treatment, though the drug remains investigational.
In the 80-week trial, participants received 4, 9, or 12 milligrams of retatrutide or a placebo. Average weight loss was 19% at the 4-milligram dose, 25.9% at 9 milligrams, and 28.3% at 12 milligrams. Those figures corresponded to about 47, 64, and 70 pounds, respectively. Placebo participants lost an average of 2.2%, or about 5.5 pounds. Among participants with a starting body mass index of at least 35, average weight loss reached 30.3%, or about 85 pounds, at 104 weeks.
The company also reported improvements in several cardiometabolic measures, including waist circumference, non-HDL cholesterol, triglycerides, blood pressure, and high-sensitivity C-reactive protein. Such measures are commonly tracked because obesity is associated with increased cardiovascular and metabolic risk.
Safety findings were broadly similar to those seen with GLP-1 medicines. Common side effects included nausea, diarrhea, constipation, vomiting, and upper respiratory tract infection. Reports of dysesthesia and urinary tract infections were generally mild to moderate and often resolved during treatment. Most participants continued therapy.
Clinicians not involved in the study said the findings are notable, but several questions remain. Longer-term data, direct comparisons with existing drugs, regulatory review, supply, and insurance coverage may affect how widely retatrutide is used if it is approved. Additional trials are expected to clarify outcomes.