Tirzepatide and Semaglutide: How Mounjaro and Ozempic Differ
Semaglutide is the active molecule in Ozempic and Wegovy. Tirzepatide is the active molecule in Mounjaro and Zepbound. Together they are the most widely studied compounds in current weight and metabolic research. They are frequently named together, yet they act differently. Since 2025 a single trial has also tested them directly against each other.
This page is educational and summarises published studies. Research compounds from NordPeps are sold strictly for laboratory work.
On this page
Summary table
| Tirzepatide | Semaglutide | |
|---|---|---|
| Brand names | Mounjaro, Zepbound | Ozempic, Wegovy, Rybelsus |
| Receptor targets | GIP + GLP-1 (dual) | GLP-1 (single) |
| Half-life | Roughly 5 days | Roughly 7 days |
| Direct comparison (SURMOUNT-5, 72 weeks) | −20.2% body weight | −13.7% body weight |
| Pivotal placebo-controlled obesity trial | −20.9% at 72 weeks (SURMOUNT-1) | −14.9% at 68 weeks (STEP-1) |
| Regulatory status | Licensed medicine | Licensed medicine |
Two receptors against one
Semaglutide works as a single agonist. Its only target is the GLP-1 receptor, which research ties to appetite, satiety and glucose regulation.
Tirzepatide works as a dual agonist. It engages the GLP-1 receptor as well as the GIP receptor. GIP is another hormone from the gut, involved in insulin secretion and energy balance. This added target is why tirzepatide is usually presented as the next step after semaglutide.
SURMOUNT-5: the direct comparison
Comparisons usually rely on placing two unrelated trials next to each other. SURMOUNT-5 avoided that. It randomised 751 adults with obesity and no diabetes to tirzepatide or semaglutide, each at the maximum dose they could tolerate, and tracked them for 72 weeks.
- Change in body weight: −20.2% on tirzepatide and −13.7% on semaglutide.
- Change in waist circumference: −18.4 cm and −13.0 cm.
- Discontinuation due to gastrointestinal side effects: 2.7% and 5.6%.
The New England Journal of Medicine published the findings in 2025.
Each compound's pivotal trial
Both molecules were also tested against placebo in a large obesity study of their own:
- Semaglutide: mean body weight −14.9% after 68 weeks (STEP-1, 2021).
- Tirzepatide: −20.9% after 72 weeks on the top dose (SURMOUNT-1, 2022).
The two studies enrolled different participants and ran for different lengths. Their results lean the same way as SURMOUNT-5, but they do not amount to a direct comparison.
Which brand is which
A single molecule may be marketed under more than one name:
- Semaglutide: Ozempic, a weekly injection for type 2 diabetes. Wegovy, a weekly injection for weight management. Rybelsus, a daily tablet for type 2 diabetes.
- Tirzepatide: Mounjaro and Zepbound. Within the EU, Mounjaro is authorised for type 2 diabetes and for weight management. Zepbound is the name used in the US for the weight-management product.
How retatrutide relates
Retatrutide goes one receptor further, adding glucagon to GLP-1 and GIP. In TRIUMPH-1 (2026), Lilly's Phase 3 trial, mean body weight fell 28.3% after 80 weeks on the highest dose. The compound remains investigational. Fuller comparisons are in retatrutide and tirzepatide compared and retatrutide or Ozempic.
Regulatory status and the research-use label
Semaglutide and tirzepatide both hold approval as medicines. NordPeps is a research supplier, not a pharmacy. Its compounds are sold for in vitro and laboratory work only, never for use in humans or animals. Ozempic, Wegovy and Rybelsus are Novo Nordisk trademarks, and Mounjaro and Zepbound are Eli Lilly trademarks. NordPeps has no affiliation with either company.
Available from NordPeps
NordPeps offers tirzepatide and semaglutide in sealed research kits of 10 or 30 vials. Prices start at €529 and kits ship free within the EU. Certificates from an independent third-party laboratory are published per batch on /certificates as they become available. For laboratory research use only.
Sources
- Aronne LJ et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). N Engl J Med 2025;393:26-36
- Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP-1). N Engl J Med 2021
- Jastreboff AM et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med 2022
- European Medicines Agency: Mounjaro EPAR, medicine overview
- Eli Lilly: TRIUMPH-1 topline results for retatrutide, 21 May 2026
- Novo Nordisk: European Commission approval of the Wegovy pill, 15 July 2026
Frequently asked questions
Is the Wegovy pill the same semaglutide as the Wegovy injection?
Yes. Both contain the same active substance, semaglutide; one is a tablet, the other an injection. The FDA approved the pill on 22 December 2025 and the European Commission on 15 July 2026.
Which shows the larger effect, tirzepatide or semaglutide?
Tirzepatide. In SURMOUNT-5, the direct comparison trial, mean weight change after 72 weeks was 20.2% with tirzepatide against 13.7% with semaglutide.
How do Mounjaro and Ozempic differ?
Mounjaro's active molecule is tirzepatide, which engages two receptors, GIP and GLP-1. Ozempic's is semaglutide, which engages only GLP-1.
Is Wegovy the same as Ozempic?
They share the same molecule, semaglutide. The difference is the licensed use: type 2 diabetes for Ozempic, weight management for Wegovy.
How does retatrutide fit into this?
Retatrutide engages three receptors (GLP-1, GIP and glucagon) and remains investigational. In the Phase 3 TRIUMPH-1 trial, mean weight fell by about 28% after 80 weeks.