Zepbound vs Wegovy: SURMOUNT-5 Settled the Debate

For years, the question of whether tirzepatide or semaglutide produces better weight loss results was answered indirectly — through cross-trial comparisons that used different patient populations, different protocols, and different endpoints. SURMOUNT-5 changed that.

Published in The New England Journal of Medicine and presented in full in 2025, SURMOUNT-5 is the first randomized, controlled, head-to-head trial directly comparing the two leading GLP-1 medications for weight loss. The result was definitive: tirzepatide (Zepbound) was statistically superior to semaglutide (Wegovy) on the primary endpoint and all five key secondary endpoints.

The Trial Design

SURMOUNT-5 was a Phase 3b, open-label, randomized clinical trial conducted at multiple centers across the United States and Puerto Rico. It enrolled 751 adults with obesity (BMI ≥30) or overweight (BMI ≥27) with at least one weight-related comorbidity — such as hypertension, dyslipidemia, obstructive sleep apnea, or cardiovascular disease — and without type 2 diabetes.

Participants were randomized 1:1 to receive either the maximum tolerated dose of tirzepatide (10 mg or 15 mg weekly) or semaglutide (1.7 mg or 2.4 mg weekly) for 72 weeks.

The Results

The magnitude of the difference is substantial. Tirzepatide produced 47% more relative weight loss than semaglutide. Nearly one-third of tirzepatide patients achieved at least 25% total body weight loss — a threshold that was reached by only about one in six semaglutide patients.

Safety and Tolerability

Both medications showed similar types of adverse events — primarily gastrointestinal (nausea, diarrhea, vomiting, constipation). However, the discontinuation patterns differed in an interesting way:

GI adverse events causing treatment discontinuation were more common with semaglutide (5.6%) than tirzepatide (2.7%). This means that semaglutide patients were more than twice as likely to stop treatment because of gastrointestinal side effects.

This finding may seem counterintuitive — if tirzepatide produces more weight loss, you might expect it to have more side effects. But the dual GLP-1/GIP mechanism of tirzepatide appears to produce a different GI profile than pure GLP-1 agonism. Clinical reports suggest that semaglutide tends to cause more nausea and constipation, while tirzepatide's GI effects lean more toward diarrhea with less nausea.

What SURMOUNT-5 Means for Your Decision

The data is clear: on a population level, tirzepatide produces more weight loss than semaglutide. If the only consideration were raw efficacy, the choice would be straightforward.

But raw efficacy is not the only consideration. Here is how to think about the decision in the real world:

When Tirzepatide (Zepbound) May Be the Better Choice

• You need to lose a significant amount of weight (BMI 35+) and want to maximize the result
• You have tried semaglutide and plateaued before reaching your goal
• You experience nausea as your primary side effect on semaglutide (tirzepatide's nausea profile may be milder)
• You have the cardiovascular risk profile data from SELECT already covered by Wegovy's indication — but want the extra weight loss

When Semaglutide (Wegovy) May Be the Better Choice

• You want an oral option — Wegovy tablets are approved for weight loss; tirzepatide does not yet have an oral formulation approved for this indication
• You are a Medicare beneficiary — both Wegovy and Zepbound KwikPen are covered under the Bridge program, but Wegovy has more formulation options (injectable + tablet)
• You want the cardiovascular risk reduction indication — Wegovy is specifically approved to reduce the risk of major adverse cardiovascular events in adults with established CVD and overweight/obesity, based on the SELECT trial. Zepbound does not yet carry this indication.
• You are responding well to semaglutide already — switching for incremental gains introduces unnecessary transition risk if you are already progressing toward your goal
• Cost is the primary factor — depending on your insurance plan and access pathways, one may be significantly cheaper than the other

The Gender Gap in SURMOUNT-5

One underreported finding from SURMOUNT-5: weight loss was approximately 6% lower in men than women in both treatment groups. The trial included a higher proportion of men (35%) than most obesity trials, and the researchers noted that this may explain why overall weight loss numbers were slightly lower in SURMOUNT-5 than in previous tirzepatide trials.

This does not mean GLP-1 medications work less well for men — but it does suggest that men may need to adjust their expectations slightly compared to the headline trial numbers, which have been disproportionately driven by female-majority study populations.

The Cardiovascular Angle

A post-hoc cardiovascular analysis published in the European Heart Journal Open in September 2025 found that tirzepatide was associated with a greater predicted 10-year cardiovascular risk reduction than semaglutide — an absolute reduction of 2.4% versus 1.4%. However, this is a post-hoc analysis based on predicted risk models, not a primary cardiovascular outcomes trial. Wegovy's SELECT trial remains the strongest direct evidence for GLP-1-mediated cardiovascular benefit.

The Bottom Line

SURMOUNT-5 answered the efficacy question: tirzepatide produces more weight loss than semaglutide. But the choice between Zepbound and Wegovy remains a clinical decision that depends on your health profile, your access pathways, your side effect experience, and your treatment goals.

The best medication is the one you can access, afford, tolerate, and stick with. For many patients, either option will produce meaningful, life-changing results. SURMOUNT-5 gives you better data to make that choice — not a mandate.