Eli Lilly's obesity drug Mounjaro (tirzepatide) has taken the lead in the U.S. market, outpacing Novo Nordisk's Wegovy (semaglutide) for the first time in Q1 this year. Clinical data have also demonstrated Mounjaro's superior weight loss effects, positioning it at the forefront of the competitive obesity treatment landscape.

According to industry reports on Wednesday, Eli Lilly unveiled results from its Phase 3b clinical study, SURMOUNT-5, showcasing Mounjaro's superior weight loss efficacy compared to the GIP/GLP-1 receptor agonist semaglutide on Monday.

The study reveals that Mounjaro participants shed an average of 22.8 kg, while Wegovy users lost an average of 15.0 kg... Mounjaro also boasted a lower treatment discontinuation rate 

Clinical results showed that the Mounjaro group achieved an average weight reduction of 20.2% over 72 weeks, surpassing semaglutide's 13.7% by 47%. In absolute terms, Mounjaro users lost an average of 22.8 kg (approximately 50.3 lbs), compared to 15.0 kg (approximately 33.1 lbs) for semaglutide users.

Eli Lilly reported that Mounjaro outperformed semaglutide in the primary endpoint and across all key secondary endpoints. Notably, 64.6% of Mounjaro patients achieved weight loss exceeding 15%, significantly higher than semaglutide's 40.1%.

Mounjaro also demonstrated superiority in reducing abdominal obesity, with users experiencing an average waist circumference reduction of 18.4 cm (approximately 7.2 in.) compared to semaglutide's 13.0 cm (approximately 5.1 in.). These findings were presented at the 32nd European Congress on Obesity (ECO) in 2025 and published in the <em>New England Journal of Medicine</em>.

Mounjaro's safety profile aligned with previous SURMOUNT studies. The most common side effects were mild to moderate gastrointestinal issues. Interestingly, Mounjaro's discontinuation rate was lower at 6.1% compared to semaglutide's 8.0%, though the study wasn't specifically designed to compare safety and tolerability.

Novo Nordisk still maintains its lead in oral obesity treatments, with FDA approval for an oral version of Wegovy earlier this year 

Eli Lilly's latest clinical results have positioned the company to reclaim market leadership in obesity treatments, potentially. In Q1, Eli Lilly reported capturing 53.3% of the U.S. market share, edging out Novo's 46.1% for the first time. This marks a significant shift in the competitive landscape, following Eli Lilly's steady market share growth over the past year.

Mounjaro's key advantage lies in its dual-action mechanism, simultaneously stimulating GIP and GLP-1 incretin receptors. This approach targets appetite suppression and blood sugar control, potentially offering broader efficacy than semaglutide's single GLP-1 receptor action.

However, Novo Nordisk still leads in the emerging oral GLP-1 treatment market. The company has already commercialized Rybelsus, the world's first oral GLP-1 drug, and recently applied for the U.S. Food and Drug Administration (FDA) approval to expand its use for obesity treatment.

Eli Lilly is currently conducting clinical trials for its oral candidate, orforglipron. While initial data looks promising, commercialization will take time. As Eli Lilly continues to gain ground in the injectable market, industry watchers are keen to see how quickly the company can close the gap with Novo Nordisk in the oral treatment sector.

Eli Lilly's obesity drug Mounjaro (tirzepatide) has taken the lead in the U.S. market, ou …

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