The headline numbers
| Mounjaro (tirzepatide) | Wegovy (semaglutide) | |
|---|---|---|
| Mechanism | Dual GIP + GLP-1 agonist | GLP-1 agonist |
| Best average weight loss | 20.9% (SURMOUNT-1, 15 mg, 72 wks) | 14.9% at 2.4 mg (STEP 1); 20.7% at 7.2 mg (STEP UP) |
| Head-to-head | SURMOUNT-5 (2025): tirzepatide 20.2% vs semaglutide 2.4 mg 13.7% over 72 weeks | |
| Cardiovascular outcomes | SURMOUNT-MMO trial ongoing | Proven: 20% fewer major CV events (SELECT) |
| Formats | Weekly KwikPen injection (2.5 to 15 mg) | Weekly injection (up to 2.4 mg; 7.2 mg approved Jan 2026) + daily pill (June 2026) |
| NHS guidance | NICE TA1026. BMI ≥35 + comorbidity; phased rollout | NICE TA875. Specialist services, max 2 years; TA1152 for CV risk |
| Typical private cost | ~£150-£350/month depending on dose | ~£130-£300/month; pill expected ~£200-£260 |
Efficacy: Mounjaro wins the weight-loss numbers
The SURMOUNT-5 trial removed all doubt about the direct comparison: at maximum tolerated doses, tirzepatide produced meaningfully greater average weight loss than semaglutide 2.4 mg (20.2% vs 13.7%). More participants also hit the big thresholds. 15%, 20%, 25% loss. If the sole question is "which moves the scales more", Mounjaro is the answer.
The 2026 wrinkle: Wegovy's new 7.2 mg dose (20.7% in STEP UP) closes much of that gap for people who plateau at 2.4 mg. Though head-to-head data against tirzepatide at that dose doesn't exist yet.
Beyond weight: Wegovy has the outcomes evidence. For now
Weight loss is not the only currency. Wegovy's SELECT trial proved a 20% reduction in heart attacks, strokes and cardiovascular death. Earning it NICE TA1152 and a unique position among weight-management medicines. Add FLOW (kidney) and STEP-HFpEF (heart failure), and semaglutide has the deeper completed outcomes portfolio. Tirzepatide's equivalent mega-trial (SURMOUNT-MMO) is still running; its proven extras so far are sleep apnoea (SURMOUNT-OSA) and HFpEF (SUMMIT). Our health benefits review has the full breakdown.
Side effects: similar profile, different texture
Both medicines share the GLP-1 signature: nausea, vomiting, diarrhoea, constipation. Worst in early weeks and after dose increases. In SURMOUNT-5, gastrointestinal events were common with both but led to discontinuation slightly less often with tirzepatide. Individual tolerance varies enormously and unpredictably: some people breeze through tirzepatide and struggle on semaglutide, others the reverse. Neither is "the gentle one" in general. Only for you specifically, which you cannot know until you try.
Practical differences that actually matter
- Formats. Needle-averse? Only Wegovy offers an escape: the daily pill (OASIS 4: 13.6 to 16.6% average loss) with strict fasting rules. Mounjaro is injection-only.
- Pen design. Mounjaro's KwikPen holds four fixed doses. One dial, always 60 clicks. Wegovy's FlexTouch varies by strength. Our Mounjaro and Wegovy click calculators cover both.
- Dose ceiling and flexibility. Mounjaro's six strengths give more room to find a personal sweet spot. Wegovy's newer 7.2 mg serves plateaued patients specifically.
- Storage. Mounjaro: 21 days below 30°C out of the fridge. Wegovy: 28 days. Both fine for travel; see our travel guides.
- NHS pathway. Tirzepatide's primary-care rollout (TA1026) is expanding; semaglutide remains specialist-service-only with a two-year cap.
So who should take which?
Maximum weight loss, injection fine: Mounjaro, on current evidence. Established heart disease: Wegovy has the proven cardiovascular outcome. Needle-phobic: the Wegovy pill is your only oral GLP-1 option. Plateaued on 2.4 mg semaglutide: 7.2 mg or a switch to tirzepatide. Prescriber conversation. Diabetes in the mix: both are licensed; your diabetes team steers. And the meta-answer: the best medicine is the one you tolerate, can access, and can afford to stay on.
Whichever route you take, buy it safely: Monj.co.uk manually verifies Mounjaro pharmacies; iGovy.co.uk does the same for Wegovy.
Monj.co.uk
An independent UK service that manually checks every pharmacy it lists. That means GPhC registration, proper prescribing and reliable cold-chain delivery, all confirmed before a pharmacy is recommended for Mounjaro.
Check verified providers → Manually verified For Wegovy injectionsiGovy.co.uk
An independent UK service that manually checks Wegovy providers. GPhC registration, genuine Novo Nordisk stock and proper refrigerated delivery are all confirmed before a provider is listed.
Check verified providers →Frequently asked questions
Is Mounjaro more effective than Wegovy? +
For average weight loss, yes. The SURMOUNT-5 head-to-head trial showed 20.2% average loss with tirzepatide versus 13.7% with semaglutide 2.4 mg over 72 weeks. Wegovy's new 7.2 mg dose (20.7% in STEP UP) narrows the gap, but no head-to-head at that dose exists yet.
Which has worse side effects. Mounjaro or Wegovy? +
Neither, overall. Both cause similar gastrointestinal effects. In SURMOUNT-5, discontinuations due to GI side effects were slightly lower with tirzepatide. Individual tolerance varies and cannot be predicted in advance.
Can I switch from Wegovy to Mounjaro? +
Yes, with prescriber supervision. Doses do not map one-to-one. Prescribers typically start tirzepatide at 2.5 mg or 5 mg regardless of your semaglutide dose, then titrate. Never switch products on your own.
Which is cheaper in the UK? +
Private prices overlap heavily (~£130-£350/month depending on medicine and dose) and change frequently. Compare cost per dose, not per month, and factor in that Mounjaro's stronger efficacy may reach a goal dose sooner. Our click calculators do the per-dose maths.
Which is easier to get on the NHS? +
Tirzepatide (Mounjaro) is rolling out via primary care under NICE TA1026 with phased eligibility; semaglutide (Wegovy) is restricted to specialist weight management services under TA875 with a two-year limit. Local availability varies for both. Ask your GP.
References & official sources
Show all 6 cited sources, with study authors +
- Aronne LJ et al. Tirzepatide as Compared with Semaglutide (SURMOUNT-5). NEJM 2025: www.nejm.org/doi/full/10.1056/NEJMoa2416394
- Jastreboff AM et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). NEJM 2022: www.nejm.org/doi/full/10.1056/NEJMoa2206038
- Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). NEJM 2021: www.nejm.org/doi/full/10.1056/NEJMoa2032183
- Lincoff AM et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT). NEJM 2023: www.nejm.org/doi/full/10.1056/NEJMoa2307563
- NICE TA1026. Tirzepatide for managing overweight and obesity: www.nice.org.uk/guidance/ta1026
- NICE TA875. Semaglutide for managing overweight and obesity: www.nice.org.uk/guidance/ta875