Semaglutide vs Tirzepatide
The two molecule families behind every major GLP-1 weight-loss brand, compared on the evidence: trial efficacy, mechanism, dosing, cost, and side effects.
Side-by-side
| Dimension | Semaglutide | Tirzepatide |
|---|---|---|
| Drug class | GLP-1 receptor agonist (single) | Dual GIP + GLP-1 receptor agonist |
| Weight-loss brand | Wegovy | Zepbound |
| Type-2 diabetes brand | Ozempic (+ oral Rybelsus) | Mounjaro |
| Manufacturer | Novo Nordisk | Eli Lilly |
| Administration | Once-weekly injection (oral Rybelsus for T2D) | Once-weekly injection |
| Pivotal weight-loss result | ~14.9% mean loss at 68 wks (STEP-1, 2.4 mg) | ~20.9% mean loss at 72 wks (SURMOUNT-1, 15 mg) |
| Head-to-head (SURMOUNT-5) | 13.7% mean loss | 20.2% mean loss — superior |
| Maintenance dose | 2.4 mg weekly (Wegovy) | 5-15 mg weekly (Zepbound) |
What the trials show
The clearest evidence is SURMOUNT-5, the first large head-to-head trial: tirzepatide (Zepbound) produced about 20.2% mean body-weight reduction versus 13.7% for semaglutide (Wegovy) at 72 weeks. That direction matches the separate pivotal trials — SURMOUNT-1 (~20.9% on tirzepatide 15 mg) and STEP-1 (~14.9% on semaglutide 2.4 mg). The leading explanation is mechanism: tirzepatide adds GIP-receptor activity on top of GLP-1, while semaglutide acts on GLP-1 alone. Trial averages are not a promise for any individual — the dose you tolerate and adherence matter more than the molecule for most people.
Which should you choose?
If maximizing average weight loss is the priority and you tolerate it, tirzepatide has the higher trial figures and won the head-to-head. Semaglutide still produces clinically meaningful loss, has a longer real-world track record, and comes in an oral form for diabetes (Rybelsus). In practice the deciding factors are often cost and insurance coverage and tolerability, not the efficacy gap. Both carry the GLP-1 class boxed warning for thyroid C-cell tumors and are contraindicated with a personal or family history of medullary thyroid carcinoma or MEN2. Bring this to a prescriber, who will match the drug to your history and titrate the dose.
Semaglutide vs tirzepatide FAQ
Is tirzepatide more effective than semaglutide for weight loss?+
In the SURMOUNT-5 head-to-head trial, tirzepatide (Zepbound) produced greater average weight loss than semaglutide (Wegovy) — about 20.2% versus 13.7% at 72 weeks. Tirzepatide also had the higher figure in separate pivotal trials (SURMOUNT-1 ~20.9% vs STEP-1 ~14.9%). Averages describe trial populations; individual response varies, and some people tolerate semaglutide better.
What is the difference between semaglutide and tirzepatide?+
Semaglutide activates one gut hormone receptor (GLP-1). Tirzepatide activates two (GIP and GLP-1), which is the leading explanation for its higher average weight loss. Semaglutide is sold as Ozempic and Rybelsus for diabetes and Wegovy for weight loss; tirzepatide is sold as Mounjaro for diabetes and Zepbound for weight loss.
Are Ozempic and Mounjaro the same as semaglutide and tirzepatide?+
Yes — Ozempic is the diabetes brand of semaglutide and Mounjaro is the diabetes brand of tirzepatide. The weight-loss brands are Wegovy (semaglutide) and Zepbound (tirzepatide). Same molecule, different brand name and FDA indication.
Which has fewer side effects, semaglutide or tirzepatide?+
Both are dominated by gastrointestinal side effects — nausea, diarrhea, constipation, vomiting — most common during dose escalation. Head-to-head, the overall side-effect profiles are broadly similar; neither is clearly gentler for everyone. Slower titration and dose adjustment are the main levers for tolerability on either drug.
Can you switch between semaglutide and tirzepatide?+
Switching is common but is not a 1:1 dose swap — a prescriber re-titrates from a low starting dose on the new drug. People often switch for tolerability, cost/insurance changes, or to try for more weight loss. Discuss timing and dosing with your clinician.
Sources
- Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). NEJM 2021. PMID: 33567185.
- Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). NEJM 2022. PMID: 35658024.
- Aronne LJ, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). NEJM 2025 Jul 3. PMID: 40353578.