Semaglutide vs tirzepatide: which works better?

In the one trial that compared them head-to-head, tirzepatide won on weight loss: adults lost about 20% of body weight on tirzepatide versus about 14% on semaglutide over 72 weeks. Tirzepatide acts on two gut hormones instead of one, which is likely why. But "better on average" is not "better for you" — side effects, history, and response decide the right choice, and that is a clinician's call.

Key takeaways

• Head-to-head (SURMOUNT-5, 2025): tirzepatide produced roughly 50% more weight loss than semaglutide.
• Semaglutide is a GLP-1 receptor agonist; tirzepatide is a dual GIP + GLP-1 agonist — the second hormone is the likely edge.
• Both are once-weekly injections with a similar, mostly gastrointestinal side-effect profile.
• Brand names: semaglutide = Wegovy/Ozempic; tirzepatide = Zepbound/Mounjaro.
• "Which is better" depends on your history, tolerance, and goals — not a leaderboard.

Semaglutide vs tirzepatide at a glance

How they work — the one-hormone vs two-hormone difference

Semaglutide mimics GLP-1, a hormone released after eating that slows stomach emptying and reduces appetite. Tirzepatide does that too, and adds GIP, a second incretin hormone. Acting on both pathways appears to produce stronger appetite reduction and metabolic effects, which is the leading explanation for its larger weight-loss numbers.

Neither works on willpower. Both work on the biology of hunger and fullness, which is why they are prescribed and monitored rather than bought and forgotten.

Which one causes more weight loss?

Tirzepatide, in the evidence to date. Each drug's own trials pointed that way — semaglutide reached about 15% in STEP 1, tirzepatide about 20%+ in SURMOUNT-1 — but those were separate studies with different participants. The 2025 SURMOUNT-5 trial removed the guesswork by comparing them directly in 751 adults with obesity: tirzepatide produced roughly 50% more weight loss (about 20% vs about 14% of body weight over 72 weeks) and a larger reduction in waist circumference (18.4 cm vs 13.0 cm). Tirzepatide also showed greater improvements in blood pressure, HbA1c, and lipids.

The caveat matters: these are averages. Plenty of people do very well on semaglutide, and the "better" drug is the one that fits your body, your tolerance, and your history.

Do they differ on side effects?

Not dramatically. Both are dominated by gastrointestinal effects — nausea, vomiting, diarrhea, constipation — that are usually worst early and eased by titrating the dose up slowly. Both share the same class contraindication: a personal or family history of medullary thyroid carcinoma or MEN 2, with caution for pancreatitis and gallbladder disease. Tolerability is individual; some people handle one better than the other, which is itself a reason the choice is clinical rather than a spec-sheet comparison.

Cost and availability

Both are branded, FDA-approved medications, and both are expensive without coverage. Availability has stabilized since the 2024–2025 shortages resolved. Compounded versions of each exist but are now tightly restricted and carry additional risk; they are not a like-for-like substitute and have only a narrow, patient-specific role when clinically appropriate. (More in Compounded vs branded GLP-1.)

So which should you take?

The honest answer: whichever a clinician chooses with you after reviewing your history, your labs, your tolerance, and your goals. Tirzepatide has the stronger head-to-head weight-loss data, but semaglutide has a longer track record and works well for many people, and the deciding factors are often individual — how you tolerate the titration, other conditions you have, and how your body responds in the first months. That is the evaluation, not a coin flip. See how OPTMZ structures it in the Weight loss program, starting with a baseline.

OPTMZ's branded GLP-1 offering is Zepbound® (tirzepatide), via LillyDirect — see the Weight program.

Educational content, medically reviewed. Not a substitute for individual medical care; treatment decisions require a clinician evaluation.

Medications are issued only when clinically appropriate after provider evaluation. OPTMZ Health connects patients with independent licensed providers and does not itself practice medicine or dispense medication.

Sources

• SURMOUNT-5: Tirzepatide versus Semaglutide for the Treatment of Obesity. New England Journal of Medicine, 2025. nejm.org
• SURMOUNT-5 summary — American College of Cardiology
• Wilding JPH et al. STEP 1 trial extension. Diabetes, Obesity and Metabolism, 2022. dom-pubs.onlinelibrary.wiley.com