Eli Lilly has announced that its new weight-loss drug, retatrutide, helped participants lose up to an average of 28.3% of their body weight in a phase three trial, outperforming existing obesity medications. The Indiana-based pharmaceutical company reported that patients receiving the highest 12mg dose lost an average of 70.3lb over 80 weeks, with 45.3% achieving at least 30% weight loss.
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 retatrutide in doses of 4mg, 9mg, 12mg, or a placebo. Those on 9mg and 12mg lost an average of 64.4lb (25.9%) and 70.3lb (28.3%), respectively, while the 4mg group lost 47.2lb (19.0%).
Dr Susan Spratt, an endocrinologist at Duke Health, described the results as “the largest weight loss I’ve ever seen in any medication trial.” The drug also helped 65.3% of participants on the 12mg dose reduce their BMI below 30, the clinical threshold for obesity, including 37.5% of those who started with a BMI of 40 or higher.
Retatrutide is a triple hormone receptor agonist, combining GLP-1, GIP, and glucagon, which work together to regulate metabolism, appetite, and energy. This sets it apart from other drugs like Eli Lilly’s Zepbound and Novo Nordisk’s Wegovy, which typically result in 15-20% and 14-19% weight loss, respectively.
Side effects included nausea, diarrhoea, constipation, and vomiting, with rates increasing at higher doses. Nausea affected 42.4% of those on the 12mg dose, compared to 14.8% on placebo. Upper respiratory tract infections were also reported more frequently in treated groups.
Lead researcher Ania Jastreboff from Yale School of Medicine noted that retatrutide produced “clinically meaningful weight reduction for nearly all participants” and improved cardio-metabolic health measures. The drug is administered as a weekly injection, with doses escalated over time.
