Mounjaro®
Starting from £179.99/mo
Start journey Learn moreHow Mounjaro and Wegovy compare on mechanism, results and eligibility
The myth worth correcting first: they're not the same drug with different branding
A lot of people assume Mounjaro and Wegovy are interchangeable, the same molecule, different names. They're not. Wegovy contains semaglutide, a GLP-1 receptor agonist, made by Novo Nordisk. Mounjaro contains tirzepatide, a dual GIP and GLP-1 receptor agonist, made by Eli Lilly, the only medicine in the UK that activates both pathways simultaneously. That second pathway, GIP, appears to add meaningfully to appetite suppression and metabolic effect. The distinction matters clinically, not just commercially. Side-effect profiles, titration schedules, drug interactions with oral contraceptives and how each medicine sits within the available weight-loss treatment options in the UK all differ. Treating them as equivalent because both involve a weekly injection is a bit like assuming all blood-pressure medicines work the same way because they come in tablet form.
Both are Black Triangle (▼) medicines under additional MHRA monitoring, and both are licensed for adults with a BMI of 30 or above, or 27 or above with at least one weight-related condition. A prescriber assesses every case individually.
What the trial numbers actually say, side by side
The numbers below are drawn from published clinical trials and NICE guidance. They describe average outcomes in trial populations; individual results vary and depend on dose reached, diet, activity and adherence.
| Factor | Mounjaro (tirzepatide) | Wegovy injection (semaglutide) |
|---|---|---|
| Mechanism | Dual GIP + GLP-1 agonist | GLP-1 agonist |
| Average weight loss (pivotal trial, highest dose) | ~20–21% at 15 mg over 72 weeks (SURMOUNT-1) | ~15% at 2.4 mg over 68 weeks (STEP 1) |
| Higher-dose option | Up to 15 mg | Up to 7.2 mg (approved by MHRA, April 2026; ~20.7% average loss at 72 weeks) |
| Head-to-head evidence | Greater average reduction in SURMOUNT-5 (NEJM, 2025) | Narrowed gap at 7.2 mg versus tirzepatide 15 mg |
| UK licence (weight management) | BMI ≥30, or ≥27 with weight-related condition | BMI ≥30, or ≥27 with weight-related condition |
| NICE recommendation (NHS route) | TA1026: BMI ≥35 + ≥1 comorbidity (phased rollout) | TA875: BMI ≥35, specialist services, max 2 years |
SURMOUNT-1 randomised 2,539 adults; figures are cited from NICE TA1026 and the published trial. The 7.2 mg Wegovy pen was approved by the MHRA on 14 April 2026. For a closer look at how the sales and prescribing patterns between the two medicines have shifted since then, this page covers the market picture.
Side effects, contraception and a few practical differences
The side-effect profile is broadly similar: nausea, vomiting, diarrhoea and constipation are the most common with both, typically sharpest in the first few weeks after starting or increasing the dose. For most people they settle. The NHS medicines page for tirzepatide lists what to watch for and when to seek help.
There is one practical difference that genuinely matters. Women taking the oral contraceptive pill should add a barrier method for the first four weeks of Mounjaro treatment and for four weeks after each dose increase, because tirzepatide slows gastric emptying and may reduce pill absorption. NHS guidance does not flag the same requirement for semaglutide. If you are on the pill, this is worth raising at consultation, it takes under a minute to check and could matter. Those on transdermal HRT (patches or gels) should discuss with a clinician before starting either medicine, though the advice is particularly noted for tirzepatide.
Storage is the same for both injections: refrigerated at 2–8°C, with a limited window at room temperature. Check the patient information leaflet for the exact figures; they are not something a content page should quote as instructions.
Which medicine suits you, and how a prescriber decides
Trial averages do not predict individual outcomes. Some people tolerate one medicine better than the other. Medical history, existing conditions, current medications and how a patient's body responds to the starter dose all feed into the prescriber's thinking. If you want to understand the clinical factors that sit behind that decision, our Mounjaro and Wegovy comparison page walks through the key differences in detail. The question is not just which produced the larger number in a trial but which is clinically appropriate for this person at this point.
Our prescribers at the nume clinical team (sorry, at the nume clinical team) review every consultation personally. If you have already tried one medicine and are curious whether switching makes sense, that conversation happens at consultation, with your medical history in front of the prescriber, not through a content page.
For a more detailed look at how the two medicines perform against each other on specific outcomes, this page looks at whether Wegovy is as effective as Mounjaro for weight loss, covering the effectiveness evidence in depth. If cost is part of your decision, the price comparison page lays out what private treatment typically costs for each. And if you want to explore all the options before deciding anything, our Mounjaro v Wegovy guide for weight loss brings together the key considerations in one place, or you can start with a free consultation, a prescriber will go through your situation with you the same day. If you are specifically weighing up how the two medicines compare on results, this guide looks at whether Wegovy is as good as Mounjaro for weight loss and sets out what the evidence currently shows.
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