Eli Lilly has announced that its experimental weight-loss drug, retatrutide, helped participants lose up to an average of 28.3% of their body weight in a phase three trial, surpassing results from existing obesity medications. The once-weekly injection, a triple hormone receptor agonist, led to an average loss of 70.3lb (31.9kg) over 80 weeks among those receiving the highest 12mg dose.
The trial involved 2,339 adults with obesity or overweight and at least one weight-related comorbidity, but without diabetes. Participants were randomised to receive 4mg, 9mg, or 12mg of retatrutide, or a placebo. Those on 9mg lost an average of 64.4lb (25.9%), while the 4mg group lost 47.2lb (19.0%). Notably, 65.3% of participants on the 12mg dose reduced their BMI below 30, the clinical threshold for obesity.
Dr Susan Spratt, an endocrinologist at Duke Health, called it “the largest weight loss I’ve ever seen in any medication trial.” The results exceed those of other drugs like Eli Lilly’s Zepbound (15-20% loss over 72 weeks) and Novo Nordisk’s Wegovy (14-19% loss over 64-72 weeks).
Retatrutide combines GLP-1 and GIP hormones, similar to Zepbound, but also includes glucagon, which helps regulate blood sugar and metabolism. Common side effects included nausea (up to 42.4% on 12mg), diarrhoea (up to 34.1%), constipation (about 25%), and vomiting (up to 25%). Upper respiratory infections occurred in around 13% of treated patients.
Lead researcher Dr Ania Jastreboff of Yale School of Medicine highlighted that “every dose resulted in clinically meaningful weight reduction” and noted improvements in cardio-metabolic health measures. The findings suggest retatrutide could offer a significant advance in obesity treatment, pending regulatory approval.
