Semaglutide vs Tirzepatide: The Head-to-Head Evidence

Two drugs, two labels

Two once-weekly injectable medicines dominate obesity treatment. Semaglutide — Wegovy for weight, Ozempic for diabetes — is a GLP-1 receptor agonist. Tirzepatide — Zepbound for weight and sleep apnea, Mounjaro for diabetes — is a GLP-1/GIP dual agonist, meaning it acts on a second incretin receptor as well. On average weight loss, tirzepatide is ahead in direct comparison. On the approved indications beyond weight, the two diverge, and for a given patient those often decide the choice. → Semaglutide · Tirzepatide · GLP-1 hub

The head-to-head data (SURMOUNT-5)

In SURMOUNT-5, in adults with obesity and without diabetes over 72 weeks, average total body-weight loss was:

• Tirzepatide: ~20.2%
• Semaglutide: ~13.7%

That is the strongest evidence on the narrow question of which drug removes more weight, and it matches each drug's own pivotal trial. STEP 1 put semaglutide 2.4 mg at ~15% mean at 68 weeks, and SURMOUNT-1 put tirzepatide at ~15% / ~19.5% / ~20.9% at 5 / 10 / 15 mg over 72 weeks.

Benefits beyond weight

Cardiovascular outcomes — semaglutide

In SELECT, semaglutide 2.4 mg reduced major adverse cardiovascular events by about 20% — heart attack, stroke and cardiovascular death — over roughly 3 years in people with established cardiovascular disease and overweight or obesity without diabetes. That is an outcome benefit rather than a weight result. Tirzepatide's cardiovascular outcome trials, SURPASS-CVOT and SURMOUNT-MMO, are still maturing, and there is no SELECT-equivalent outcomes claim yet. Where proven cardiovascular protection is the priority, semaglutide holds the evidence. → Obesity & Cardiovascular Health Grade A 🟢

Liver and MASH — semaglutide

Semaglutide 2.4 mg is FDA-approved for noncirrhotic MASH with F2–F3 fibrosis under accelerated approval, on the basis of the ESSENCE programme. Tirzepatide improved MASH resolution in SYNERGY-NASH but is not FDA-approved for MASH. Where fibrotic fatty liver is a main driver, semaglutide is the approved option today. → GLP-1 & Fatty Liver Grade A 🟢 (semaglutide MASH approval) / B 🟡 (tirzepatide liver data)

Sleep apnea — tirzepatide

Tirzepatide is FDA-approved for moderate-to-severe obstructive sleep apnea in adults with obesity, after SURMOUNT-OSA reduced the apnea-hypopnea index. Semaglutide does not hold this indication. Grade A 🟢

An oral route — semaglutide

Semaglutide is available without a needle: the newly approved oral 25 mg tablet for weight management, the first oral GLP-1 for obesity, alongside oral Rybelsus for diabetes. Tirzepatide is injectable only. Grade B 🟡

Side by side

Where the two drugs behave alike

Tolerability is broadly similar. Both carry the class side-effect profile, predominantly gastrointestinal — nausea, diarrhea, constipation, vomiting — worst during dose escalation and improving over time, with gallbladder disease less commonly, pancreatitis rarely, and dehydration where GI symptoms are severe. Both carry the MTC/MEN2 boxed warning, both advise avoiding pregnancy, and both require a perioperative hold for delayed gastric emptying. The one labeled difference is that tirzepatide can reduce oral-contraceptive effectiveness around initiation and dose increases, for which a backup or non-oral method is advised for the first weeks. No test predicts who will tolerate one better than the other. → GLP-1 Side Effects Grade B 🟡

Body composition behaves the same way on both. Like all substantial weight loss, each drug reduces fat-free mass alongside fat; most of the loss is fat, and a DXA lean-mass number is not a measure of skeletal muscle or of strength. Neither drug is uniquely muscle-sparing or muscle-wasting, and resistance training with adequate protein is what protects muscle and function on either. A muscle claim is not a reason to prefer one. → GLP-1 & Muscle Loss Grade C 🟠

Stopping behaves the same way too. The withdrawal trials — STEP 4 for semaglutide and SURMOUNT-4 for tirzepatide — point the same direction: continuing the drug maintains the loss, and switching to placebo brings substantial regain as the defended set point reasserts itself. The STEP 1 extension showed participants regained roughly two-thirds of lost weight within about a year of stopping. Neither drug is a temporary kickstart; both are treatment for a chronic disease, and maintenance belongs in the plan before the first dose. → Weight Regain & Maintenance Grade A 🟢

Matching the drug to the driver

• Maximum average weight loss — head-to-head data favour tirzepatide.
• Proven cardiovascular event reduction, as in established heart disease — semaglutide (SELECT).
• MASH with fibrosis — semaglutide, the approved option today.
• Moderate-to-severe sleep apnea with obesity — tirzepatide, which holds the OSA indication.
• A preference against injections — semaglutide, as the oral 25 mg tablet.
• Oral contraception in use — tirzepatide's labeled OCP interaction applies.
• Tolerability, other conditions, pregnancy plans, insurance coverage and supply decide the question more often than any percentage does.

What the evidence says: semaglutide vs tirzepatide

• What we know: tirzepatide produced greater average weight loss head-to-head, ~20.2% against ~13.7%. Semaglutide has proven cardiovascular-event reduction and a MASH approval; tirzepatide has the OSA approval; semaglutide has an oral form. Grade A 🟢
• What we think: in our practice the condition that one drug uniquely addresses usually matters more than the gap in average weight loss.
• What we don't know: tirzepatide's cardiovascular-outcome and MASH-approval status, with trials maturing; very-long-term outcomes for both; and who tolerates which drug better.
• What follows clinically: the choice runs on goals and coexisting conditions rather than the headline percentage, with muscle protected and maintenance planned from the start.

Which of the two suits a particular person is the kind of question we work through in an individual assessment at the practice. → Should I Take a GLP-1?

Questions patients ask

Written by Darius A. Schneider, MD, PhD · Board-Certified Endocrinologist (ECNU) · Last updated: Oct 2026 · References: SURMOUNT-5 head-to-head; STEP 1/2/4; SURMOUNT-1/4; SELECT (CV outcomes); ESSENCE and SYNERGY-NASH (MASH); SURMOUNT-OSA; FDA prescribing information for Wegovy/Ozempic and Zepbound/Mounjaro. Educational; not individualized medical advice.