A study published in JAMA Internal Medicine compared the weight loss effectiveness of Eli Lilly's Zepbound (tirzepatide) and Novo Nordisk's Wegovy (semaglutide), as well as Eli Lilly's Mounjaro and Novo Nordisk's Ozempic.

The study analyzed electronic health records of over 18,000 adults and found Mounjaro more effective in helping patients lose weight faster and achieve milestones such as losing at least 5%, 10%, and 15% of their initial weight compared to Ozempic.

Mounjaro users were more likely to experience greater weight loss throughout the first year of treatment.

Both Mounjaro and Ozempic work by mimicking the gut hormone GLP-1, but Mounjaro additionally stimulates a second gut hormone called GIP, potentially explaining its superior weight loss effects.

Novo Nordisk has secured a label expansion for Wegovy to include cardiovascular benefits, while Eli Lilly needs to collect data to prove similar benefits for Zepbound and Mounjaro.

Despite Ozempic showing broader positive effects beyond weight loss, tirzepatide (Mounjaro) has been more effective for glucose control and weight loss.

Eli Lilly faces the challenge of increasing the adoption of tirzepatide over Ozempic in clinical practice and among patients, with further research needed to understand differences in other important outcomes.