Tirzepatide vs Semaglutide: Mounjaro vs Ozempic, Compared
Semaglutide (the molecule in Ozempic and Wegovy) and tirzepatide (the molecule in Mounjaro and Zepbound) are the two most widely used compounds in today's weight and metabolic research. They are often mentioned in the same breath, but they work differently, and since 2025 there is a trial that put them directly side by side.
Everything here is educational and refers to published research. RetaNord supplies research compounds for laboratory research use only.
On this page
At a glance
| Tirzepatide | Semaglutide | |
|---|---|---|
| Brand names | Mounjaro, Zepbound | Ozempic, Wegovy, Rybelsus |
| Receptors | GIP + GLP-1 (dual) | GLP-1 (single) |
| Half-life | About 5 days | About 7 days |
| Head-to-head (SURMOUNT-5, 72 weeks) | −20.2% body weight | −13.7% body weight |
| Own main obesity trial | −20.9% at 72 weeks (SURMOUNT-1) | −14.9% at 68 weeks (STEP-1) |
| Status | Approved medicine | Approved medicine |
One receptor versus two
Semaglutide is a single agonist: it activates the GLP-1 receptor, which is linked to appetite, fullness and blood-sugar control.
Tirzepatide is a dual agonist: it activates the GLP-1 receptor and the GIP receptor. GIP is a second gut hormone that also takes part in insulin release and energy balance. Adding it is the reason tirzepatide is described as a step beyond semaglutide.
The head-to-head trial: SURMOUNT-5
Most comparisons have to set two separate trials side by side. SURMOUNT-5 is different: it gave 751 adults with obesity (and without diabetes) either tirzepatide or semaglutide at the highest dose they tolerated, and followed them for 72 weeks.
- Body weight: −20.2% with tirzepatide vs −13.7% with semaglutide.
- Waist: −18.4 cm vs −13.0 cm.
- Stopping because of stomach side effects: 2.7% vs 5.6%.
The results were published in the New England Journal of Medicine in 2025.
Their own main trials
Each molecule also has its own large obesity trial against placebo:
- Semaglutide: −14.9% mean body weight at 68 weeks (STEP-1, 2021).
- Tirzepatide: −20.9% at 72 weeks at the highest dose (SURMOUNT-1, 2022).
These are separate studies with different people and lengths, so they point the same way as SURMOUNT-5 but are not a direct comparison.
The brand names, explained
One molecule can be sold under several names:
- Semaglutide: Ozempic (type 2 diabetes, weekly injection), Wegovy (weight management, weekly injection) and Rybelsus (type 2 diabetes, daily tablet).
- Tirzepatide: Mounjaro and Zepbound. In the EU, Mounjaro is authorised for both type 2 diabetes and weight management; Zepbound is the US name for the weight-management version.
Where retatrutide fits
Retatrutide adds a third receptor, glucagon, to GLP-1 and GIP. In Lilly's Phase 3 trial TRIUMPH-1 (2026) it reached −28.3% average body weight at 80 weeks at the top dose. It is still investigational. Read Retatrutide vs Tirzepatide and Ozempic vs Retatrutide for the full comparisons.
Approval status and “research use only”
Semaglutide and tirzepatide are approved medicines. RetaNord is not a pharmacy: it supplies research-grade compounds for laboratory and in-vitro research use only, not for human or veterinary use. Ozempic, Wegovy and Rybelsus are trademarks of Novo Nordisk; Mounjaro and Zepbound are trademarks of Eli Lilly. RetaNord is not affiliated with either company.
At RetaNord
RetaNord supplies tirzepatide and semaglutide as sealed 10- or 30-vial research kits from €559, each with a Certificate of Analysis and free EU shipping. Supplied for laboratory research use only.
Sources
- Aronne et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). N Engl J Med 2025;393:26-36
- Wilding et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP-1). N Engl J Med 2021
- Jastreboff 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, 21 May 2026
Frequently asked questions
Is tirzepatide stronger than semaglutide?
In the head-to-head SURMOUNT-5 trial, tirzepatide led to a larger average weight loss than semaglutide: 20.2% versus 13.7% after 72 weeks.
What is the difference between Mounjaro and Ozempic?
Mounjaro contains tirzepatide, which acts on two receptors (GIP and GLP-1). Ozempic contains semaglutide, which acts on one (GLP-1).
Are Ozempic and Wegovy the same?
Both contain semaglutide. Ozempic is approved for type 2 diabetes and Wegovy for weight management.
Where does retatrutide fit in?
Retatrutide acts on three receptors (GLP-1, GIP and glucagon). It is still investigational; in the Phase 3 trial TRIUMPH-1 it reached about 28% average weight loss at 80 weeks.