A large Phase 3B clinical trial has found that tirzepatide (sold as Mounjaro) produces significantly greater weight loss than semaglutide in adults with obesity or overweight who do not have diabetes. The SURMOUNT-5 trial, published in the New England Journal of Medicine, is the first direct head-to-head comparison of these two widely used weight-loss drugs at their maximum approved doses.

What the Trial Found

Over 72 weeks, 750 participants were randomly assigned to either tirzepatide or semaglutide, with all participants also receiving lifestyle support including diet and exercise guidance. Those on tirzepatide lost an average of 21.6% of their body weight, compared to 15.4% for semaglutide — a difference of roughly 6 percentage points. Waist circumference also shrank more on tirzepatide: 20 cm versus 14.7 cm on semaglutide.

The gap between the two drugs was most visible at higher weight-loss thresholds. Among tirzepatide users, 36.2% lost at least 25% of their body weight, compared to 19.4% on semaglutide. Proportionally more tirzepatide patients also crossed the 10%, 15%, and 20% weight-loss marks. Both drugs showed side effect profiles consistent with earlier studies, with gastrointestinal issues — nausea, vomiting, diarrhea — being the most commonly reported.

Why the Mechanism Matters

The two drugs work through related but distinct biological pathways. Semaglutide targets a single hormone receptor (GLP-1), which regulates appetite and blood sugar. Tirzepatide targets two receptors — GLP-1 and GIP — a dual-action approach that appears to produce stronger appetite suppression and greater fat loss. This dual mechanism is the most likely explanation for the performance gap seen in SURMOUNT-5.

Obesity is increasingly classified as a chronic, relapsing disease rather than a lifestyle failure. Global prevalence is projected to reach 1.9 billion people by 2030. Diet and exercise alone often fail to sustain weight loss because the body adjusts its metabolism to defend its original weight — a well-documented biological response. That is the core reason pharmacological treatment is gaining acceptance as a standard tool, not a last resort.

In India, Mounjaro (tirzepatide) is approved for weight management in adults with a BMI of 30 or above, or 27 and above if they have at least one related health condition such as hypertension, sleep apnoea, or prediabetes. It is also approved for type 2 diabetes treatment. The drug is available only on prescription from an endocrinologist or internal medicine specialist.

For the broader obesity drug market, SURMOUNT-5 strengthens tirzepatide's clinical positioning over semaglutide-based drugs like Wegovy and Ozempic. Eli Lilly, which makes Mounjaro, now has direct trial evidence of superiority — a meaningful commercial and regulatory asset. The results are likely to influence prescribing decisions globally as physicians choose between the two drug classes for patients without diabetes seeking weight management.