Mounjaro®
Starting from £179.99/mo
Start journey Learn moreHow the two medicines compare: mechanism, evidence and what that means in practice
Step 1: understand what each medicine actually does
Mounjaro is a dual GIP and GLP-1 receptor agonist. It binds to receptors for two different gut hormones involved in appetite regulation and blood-sugar control, slowing gastric emptying and increasing feelings of fullness. It is the only dual-agonist weight-loss medicine licensed in the UK. The NHS tirzepatide medicines page outlines how it works at a patient level.
Wegovy is a GLP-1 receptor agonist, activating a single pathway. It mimics the GLP-1 hormone to reduce appetite and slow digestion. Both share a broadly similar side-effect profile dominated by gastrointestinal symptoms, and both require once-weekly subcutaneous injection via a pre-filled pen. The mechanism difference sounds technical, but its practical significance is the efficacy data it produces.
A quick thing any reader can do: look up either medicine on the electronic Medicines Compendium and compare the approved indications and contraindications side by side in under a minute. Worth doing before your consultation.
Step 2: read what the clinical trials actually found
The SURMOUNT-1 trial (2,539 adults with obesity, 72 weeks) reported around 20–21% average body-weight reduction at the highest dose of tirzepatide. The STEP 1 trial for semaglutide 2.4mg (68 weeks) showed approximately 15% average reduction. Those figures come from the NEJM SURMOUNT-1 paper and the equivalent STEP 1 publication.
The more direct comparison comes from SURMOUNT-5, a head-to-head open-label trial (72 weeks, 751 adults with obesity, no diabetes) published in the New England Journal of Medicine in 2025, and if you want a thorough breakdown of what that trial means in practice, our guide to Wegovy v Mounjaro walks through the evidence in detail. Tirzepatide produced greater average weight reduction than semaglutide 2.4mg. NICE's appraisal of tirzepatide (TA1026) notes that indirect comparisons also favour tirzepatide, though the committee acknowledged the limitations of cross-trial comparison.
It is also worth noting that a higher Wegovy dose, 7.2mg, received MHRA approval in 2026 and reported approximately 20.7% average weight loss over 72 weeks, narrowing the gap with tirzepatide considerably. So the picture is not static.
Step 3: compare eligibility, NICE criteria and NHS access
| Factor | Mounjaro (tirzepatide) | Wegovy (semaglutide) |
|---|---|---|
| Mechanism | Dual GIP + GLP-1 agonist | GLP-1 agonist |
| Average weight loss (pivotal trial) | ~20–21% at 15mg (SURMOUNT-1, NEJM) | ~15% at 2.4mg (STEP 1, NEJM) |
| NICE recommendation | TA1026: BMI ≥35 + ≥1 comorbidity (private licence: ≥30 or ≥27 with condition) | TA875: BMI ≥35 + ≥1 comorbidity, max 2 years, specialist service |
| Private licence (adults) | BMI ≥30, or ≥27 with a weight-related condition | BMI ≥30, or ≥27 with a weight-related condition |
| Administration | Once-weekly injection, pre-filled KwikPen | Once-weekly injection, pre-filled pen |
| Oral option available? | No | Yes, Wegovy tablets (MHRA-approved June 2026) |
If you are curious about how costs compare across both treatments, our guide to Wegovy versus Mounjaro pricing covers that in detail. Neither treatment's per-pen price appears in this article, by the time you read this, market prices will have moved, and the consultation page always reflects current figures.
Step 4: think about what matters most for your situation
Efficacy data matters, but it is not the whole story. Tolerability, your medical history, any medicines you already take and whether you prefer an injection or a tablet all feed into the clinical picture. Tirzepatide has an additional consideration for women using oral contraceptives: the NHS England weight-management guidance advises adding a non-oral contraceptive method for the first four weeks of treatment and for four weeks after each dose increase, because absorption of the pill may be reduced. No equivalent evidence exists for semaglutide in this respect.
Some people who have already started one medicine and want to move to the other ask about switching. That is a separate clinical question, and readers who want a side-by-side look at both options before making that call may find our Wegovy bs Mounjaro comparison a useful starting point alongside the guide on moving from Mounjaro to Wegovy and the clinical considerations for that transition. Switching always requires a prescriber's sign-off and, at nume, that means a fresh review before anything changes.
Neither medicine is suitable in pregnancy, while breastfeeding, or when trying to conceive. Both are licensed for adults only. History of pancreatitis or certain gastrointestinal conditions requires discussion with the prescriber before starting. Our FAQ page covers other common eligibility questions, and Romanian-speaking patients can also consult our Mounjaro sau Wegovy guide for a detailed overview in their language, while our clinical team is the right place to look if you want to understand who reviews these decisions at nume.
Which suits you is a clinical decision our prescribers make with you, not something any article can determine. Start your free consultation and a GPhC-registered Independent Prescriber will review your answers the same day.
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