Short answer: In SURMOUNT-5, the only head-to-head obesity trial, adults without diabetes on tirzepatide (Zepbound) lost 20.2% of body weight at 72 weeks versus 13.7% on semaglutide (Wegovy).1 Semaglutide acts on the GLP-1 receptor; tirzepatide acts on both GIP and GLP-1 receptors. Both are once-weekly injections with a boxed thyroid C-cell tumor warning.
This page focuses on the SURMOUNT-5 numbers and the label facts side by side. For the wider story (STEP-1, SURMOUNT-1, SURPASS-2, cost and insurance), see the Ozempic vs Mounjaro blog post. If you are moving from one to the other, see Switching from semaglutide to tirzepatide: is there a conversion?.
| Semaglutide (Wegovy, Ozempic) | Tirzepatide (Zepbound, Mounjaro) | |
|---|---|---|
| Mechanism | GLP-1 receptor agonist2 | GIP and GLP-1 receptor agonist3 |
| Approval status | FDA approved: Ozempic (type 2 diabetes), Wegovy (weight management; injection and tablets) | FDA approved: Mounjaro (type 2 diabetes), Zepbound (weight management, obstructive sleep apnea) |
| Label dosing schedule (weight management) | Wegovy: 0.25 mg weekly for 4 weeks, then 0.5, 1 and 1.7 mg at 4-week steps; maintenance 1.7 or 2.4 mg, up to 7.2 mg after at least 4 weeks on 2.4 mg2 | Zepbound: 2.5 mg weekly for 4 weeks, then 5 mg, then up by 2.5 mg at least 4 weeks apart; maintenance 5, 10 or 15 mg3 |
| Half-life | about 7 days (label: about 1 week)4 | about 5 days (Zepbound label: about 5 to 6 days)3 |
| Time to peak (Tmax) | 1 to 3 days after an injection4 | Median 24 hours, range 8 to 72 hours3 |
| Dosing frequency | Once weekly (Wegovy tablets: once daily) | Once weekly |
| Pen / vial strengths | Wegovy single-dose pens 0.25, 0.5, 1, 1.7, 2.4 and 7.2 mg (Wegovy HD); Ozempic pens deliver 0.25/0.5, 1 or 2 mg2 | Single-dose pens or vials 2.5, 5, 7.5, 10, 12.5 and 15 mg; multi-dose KwikPens (4 doses)5 |
| Missed dose (label) | Ozempic: take within 5 days; Wegovy: take if the next dose is more than 2 days away | Take within 4 days (96 hours) |
| Notable label warnings | Boxed: thyroid C-cell tumors. Pancreatitis, gallbladder disease, kidney injury, hypoglycemia with insulin or sulfonylureas, diabetic retinopathy complications, aspiration under anesthesia | Boxed: thyroid C-cell tumors. Pancreatitis, gallbladder disease, kidney injury, hypoglycemia with insulin or sulfonylureas, severe GI reactions, aspiration under anesthesia |
SURMOUNT-5 was an open-label phase 3b trial in 751 adults with obesity and no type 2 diabetes. Each person took the maximum tolerated dose of tirzepatide (10 or 15 mg) or semaglutide (1.7 or 2.4 mg) once weekly for 72 weeks.1
Both drugs were stepped up every 4 weeks in the trial: tirzepatide 2.5 → 5 → 7.5 → 10 → 12.5 → 15 mg, semaglutide 0.25 → 0.5 → 1.0 → 1.7 → 2.4 mg.6 The trial did not test Wegovy 7.2 mg, which FDA approved in March 2026, after it was run.7
Both have long half-lives: about a week for semaglutide and about 5 days for tirzepatide. Each weekly dose adds to what is still in your body, so levels build up for the first several weeks of a given dose before they level off. Semaglutide's longer half-life also means it takes longer to wash out after the last dose, which matters when changing from one to the other.
That is a decision for you and your prescriber. The trial numbers above are group averages, and individual results and side effects vary. Insurance coverage, other conditions (for example cardiovascular disease, sleep apnea or diabetes) and how you tolerate each drug often decide it.