Mounjaro (tirzepatide) and Ozempic (semaglutide) are the two most-prescribed incretin agonists in the world. They share a receptor target — GLP-1 — but diverge in mechanism, dosing, and outcomes. This side-by-side compares them across every dimension that matters in research literature.
Mechanism — one receptor vs two
Ozempic (semaglutide) is a single-receptor agonist. It activates only the GLP-1 receptor. Mounjaro (tirzepatide) is a dual agonist that activates both GLP-1 and GIP receptors. The GIP arm adds insulin sensitisation and may attenuate gastrointestinal side effects.
Structural comparison
| Attribute | Semaglutide | Tirzepatide |
|---|---|---|
| Length | 30 amino acids | 39 amino acids |
| Receptors | GLP-1 | GLP-1 + GIP |
| Albumin linker | C18 fatty acid via Glu | C20 fatty diacid via γ-Glu-2xAEEA |
| Half-life | ~7 days | ~5 days |
Dosing schedules — diabetes indication
| Compound | Starting dose | Maintenance range |
|---|---|---|
| Semaglutide (Ozempic) | 0.25 mg weekly | 0.5–2.0 mg weekly |
| Tirzepatide (Mounjaro) | 2.5 mg weekly | 5–15 mg weekly |
SURPASS-2 — the direct head-to-head trial
The SURPASS-2 trial (Frias et al., NEJM 2021) is the definitive comparison. Adults with type 2 diabetes received either tirzepatide (5, 10, or 15 mg weekly) or semaglutide 1 mg weekly for 40 weeks. Results:
| Endpoint | Semaglutide 1mg | Tirzepatide 5mg | Tirzepatide 10mg | Tirzepatide 15mg |
|---|---|---|---|---|
| HbA1c reduction | -1.86% | -2.09% | -2.37% | -2.46% |
| Weight loss | -5.7 kg | -7.6 kg | -9.3 kg | -11.2 kg |
Tirzepatide outperformed semaglutide on both glycaemic and weight endpoints at all three doses. The 15 mg arm produced approximately twice the weight loss of the 1 mg semaglutide reference arm.
Weight loss in obesity research
Indirect comparison from STEP 1 vs SURMOUNT-1:
- Semaglutide 2.4 mg weekly: 14.9% body weight loss at 68 weeks (STEP 1)
- Tirzepatide 15 mg weekly: 22.5% body weight loss at 72 weeks (SURMOUNT-1)
Direct head-to-head obesity trials are pending. The indirect comparison strongly favours tirzepatide for weight endpoints.
Side effect profile
Both molecules show similar adverse event categories — predominantly gastrointestinal. Some research suggests tirzepatide’s GIP activation may reduce nausea incidence at equivalent GLP-1 efficacy, but head-to-head adverse event data is limited.
Pharmacokinetic differences
- Tirzepatide reaches steady state faster (~4 weeks) than semaglutide (~5 weeks)
- Both support weekly dosing
- Both are cleared primarily through proteolytic degradation, with minor renal clearance
When semaglutide is preferred in research
- Longer-established safety record (more years of post-marketing data)
- Oral formulation available (Rybelsus)
- Lower cost per mg in regulated markets
- Studies specifically modelling GLP-1 monotherapy
When tirzepatide is preferred in research
- Maximum weight loss endpoint
- Combined glycaemic + weight outcome modelling
- Lower nausea profile per equivalent efficacy
- Studies testing dual-incretin hypothesis
Stability and handling
Both molecules are supplied lyophilised. Both reconstitute in bacteriostatic water at 5–10 mg/mL. Tirzepatide’s longer sequence is more sensitive to freeze-thaw cycles. See our reconstitution protocol guide.
Chempeptides supplies both with batch-specific CoA — see the catalogue.
Research use only.