At A Glance: The Key Verdict
- Higher Average Weight Loss: Mounjaro delivered up to 20.9% body weight reduction in the 72-week SURMOUNT-1 trial, compared to up to 14.9% for Wegovy in the 68-week STEP-1 trial.
- Mechanism Difference: Mounjaro targets two receptors (GIP + GLP-1), while Wegovy is a single GLP-1 receptor agonist.
- Cardiovascular Track Record: Wegovy has extensive multi-year cardiovascular outcome data (SELECT trial) demonstrating a 20% reduction in major adverse cardiovascular events.
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Head-to-Head Comparison Table
| Feature | Mounjaro (Tirzepatide) | Wegovy (Semaglutide) |
|---|---|---|
| Drug Class | Dual GIP & GLP-1 Receptor Agonist | GLP-1 Receptor Agonist |
| Manufacturer | Eli Lilly | Novo Nordisk |
| Frequency | Once weekly subcutaneous injection | Once weekly subcutaneous injection |
| Avg Weight Loss (Trial) | Up to 20.9% (SURMOUNT-1, 72 wks) | Up to 14.9% (STEP-1, 68 wks) |
| Dosing Range | 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg, 15mg | 0.25mg, 0.5mg, 1.0mg, 1.7mg, 2.4mg |
| UK Device Type | KwikPen (multi-dose pre-filled pen) | FlexTouch (multi-dose pre-filled pen) |
| NICE Approval Status | Approved (TA940) | Approved (TA875) |
| Direct Online Assessment | Order Mounjaro via Click Pharmacy → | Order Wegovy via Click Pharmacy → |
Understanding the Clinical Evidence: SURMOUNT vs STEP
Both medications have undergone extensive Phase 3 randomized, double-blind clinical trials involving thousands of non-diabetic adults with overweight and obesity:
SURMOUNT-1 (Mounjaro / Tirzepatide)
Published in the New England Journal of Medicine (NEJM), SURMOUNT-1 monitored 2,539 adults over 72 weeks:
- • 5mg dose: 15.0% average weight reduction
- • 10mg dose: 19.5% average weight reduction
- • 15mg top dose: 20.9% average weight reduction (approximately 23.6 kg / 52 lbs)
- • 91% of participants achieved at least 5% weight loss.
STEP-1 (Wegovy / Semaglutide)
Also published in the NEJM, the landmark STEP-1 trial evaluated 1,961 adults over 68 weeks:
- • 2.4mg maintenance dose: 14.9% average weight loss
- • Placebo group lost an average of 2.4%
- • 86% of participants achieved at least 5% body weight reduction
- • Proven long-term cardiovascular safety in the SELECT trial.
Which Medication Should You Choose?
Selecting between Mounjaro and Wegovy is an individual clinical decision made with a registered prescriber. Consider the following factors:
Consider Mounjaro (Tirzepatide) if:
You are looking for the highest clinically proven average weight loss percentage, or if you previously took a GLP-1 medication (like Saxenda or Wegovy) and hit an early weight plateau.
Consider Wegovy (Semaglutide) if:
You prefer a treatment backed by extensive cardiovascular outcome data, or if your healthcare provider recommends starting on a single-receptor GLP-1 therapy.
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Frequently Asked Questions
Which is more effective for weight loss: Mounjaro or Wegovy? ↓
In clinical trials, Mounjaro (tirzepatide) showed higher average total weight loss of up to 20.9% at the 15mg dose (SURMOUNT-1), compared to an average of up to 14.9% with Wegovy (semaglutide 2.4mg in the STEP-1 trial).
Can you switch from Wegovy to Mounjaro in the UK? ↓
Yes, patients can switch under clinical supervision. In most cases, prescribers recommend starting Mounjaro at the baseline 2.5mg dose or an equivalent step after a short washout period to minimise gastrointestinal side effects.
Are Mounjaro and Wegovy available on the NHS? ↓
Both Wegovy (NICE TA875) and Mounjaro (NICE TA940) have received NICE approval in England and Wales for specialist Tier 3/4 weight management services. Due to waiting lists and strict eligibility, many UK patients access treatment through GPhC-registered private online pharmacies like Click Pharmacy.