Mounjaro vs Wegovy UK 2026: Which Weight Loss Injection Is Right for You?
Mounjaro and Wegovy are the UK's leading prescription weight-loss injections. We compare effectiveness, cost, side effects, and suitability to help you choose.
Mounjaro (tirzepatide) and Wegovy (semaglutide) are the two leading prescription weight loss injections available in the UK in 2026. Both are highly effective, both require a clinical assessment and prescription, and both are available on the NHS in certain circumstances — but there are important differences. This guide compares them head-to-head.
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Quick Comparison
| Factor | Mounjaro (tirzepatide) | Wegovy (semaglutide) |
|---|---|---|
| Drug class | GIP/GLP-1 dual agonist | GLP-1 receptor agonist |
| Average weight loss | ~22.5% (15mg, 72 weeks) | ~15% (2.4mg, 68 weeks) |
| Injection frequency | Once weekly | Once weekly |
| Private starting price (UK) | From £119.95 per pen | From £75 per pen |
| NHS availability | Yes (Cohorts 1 and 2, June 2026) | Yes (specialist services) |
| Common side effects | Nausea, diarrhoea, vomiting, fatigue | Nausea, diarrhoea, vomiting, fatigue |
How They Work
Wegovy (semaglutide) is a GLP-1 receptor agonist — it mimics the GLP-1 hormone that regulates appetite and blood sugar. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating both pathways. This dual action is thought to explain why it produces greater average weight loss than semaglutide alone. Both are administered as a weekly subcutaneous injection using a pre-filled auto-injector pen, starting low and increasing gradually to minimise side effects.
Weight Loss Results: Mounjaro Leads on Average
Clinical trial data consistently shows Mounjaro producing greater average weight loss: 22.5% on Mounjaro 15mg (SURMOUNT-1, 72 weeks) vs 14.9% on Wegovy 2.4mg (STEP-1, 68 weeks). The SURMOUNT-5 head-to-head trial confirmed tirzepatide patients lost 47% more body weight than those on semaglutide 2.4mg. Individual results vary significantly — averages describe trial populations, not guarantees for any one person.
Side Effects: Very Similar
Both drugs slow gastric emptying, so their side effect profiles overlap heavily: nausea, vomiting, diarrhoea, constipation and fatigue are common with both, especially when starting or increasing dose. Both carry a small risk of pancreatitis. Side effects typically improve after the first few weeks as your body adjusts. Some patients tolerate one better than the other — this is highly individual and worth discussing with your prescriber if you've had a poor experience with one.
Cost Comparison (UK, August 2026)
| Drug & dose | Cheapest price (UK) |
|---|---|
| Mounjaro 2.5mg (starter) | From £119.95 per pen |
| Mounjaro 15mg (maximum) | From £266 per pen |
| Wegovy 0.25mg (starter) | From £75 per pen |
| Wegovy 2.4mg (maximum) | From £135 per pen |
Wegovy is typically cheaper for equivalent doses; Mounjaro delivers greater average weight loss per pound spent according to clinical data. MedEazy compares prices from verified, GPhC-registered UK pharmacies daily: Mounjaro price comparison | Wegovy price comparison.
NHS Availability
Both drugs are available on the NHS through specialist weight management services, though access remains gradual. Mounjaro: NHS Cohort 1 (BMI 40+, 1 condition) and Cohort 2 from June 2026 (BMI 35–39.9, 4 conditions). Wegovy: available through NHS specialist services with similar BMI and clinical thresholds. Most people currently access both medicines privately while waiting. See our Mounjaro NHS eligibility guide for full detail.
Which Should You Choose?
There's no universal answer. If maximum average weight loss is the priority and cost is less of a concern, Mounjaro has the strongest clinical evidence. If budget is the primary driver, Wegovy has a lower starting price. If you've previously used semaglutide (e.g. Ozempic for diabetes) and tolerated it well, Wegovy may be a natural continuation. If you've tried semaglutide and had a poor response, Mounjaro's dual mechanism may work differently for you. Always discuss your options with a registered prescriber — the right choice depends on your health history, BMI, goals and any contraindications.
Frequently Asked Questions
Is Mounjaro better than Wegovy?
Clinical trials show Mounjaro produces greater average weight loss (22.5% vs 14.9%). However, both are highly effective and the better choice depends on individual tolerance, cost and availability.
Is Mounjaro cheaper than Wegovy in the UK?
Mounjaro's starter dose is generally more expensive than Wegovy's starter dose (£119.95 vs £75), but the gap narrows at higher doses. Use our price comparison tools for live pricing.
Can I switch from Wegovy to Mounjaro?
Yes, patients do switch between these medications, but this should always be done under the guidance of a prescriber. See our guide to switching weight loss treatments.
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