Mounjaro®
Starting from £179.99/mo
Start journey Learn moreWhat the evidence, the licences and your individual health actually tell us
How do tirzepatide and Wegovy work differently?
Wegovy contains semaglutide, a GLP-1 receptor agonist. It mimics a gut hormone that signals fullness to the brain, slows the rate at which the stomach empties, and damps appetite. It targets one receptor pathway. Tirzepatide (sold in the UK as Mounjaro) adds a second mechanism: it activates both the GLP-1 and GIP receptors simultaneously. GIP is a separate gut hormone involved in energy storage and appetite regulation, and the combined action appears to amplify the effect on body weight beyond what either pathway achieves alone.
That dual-receptor action makes Mounjaro the only medicine of its kind currently licensed in the UK for weight management. For a fuller look at where tirzepatide and semaglutide overlap and diverge in mechanism, our comparison of tirzepatide and semaglutide covers the pharmacology in more detail. Whether that biological distinction translates into a meaningful difference for your weight and health is what the trial data (and your prescriber) address.
What does the head-to-head evidence actually show?
For years, Mounjaro and Wegovy were compared only indirectly, across separate trials with different populations. That changed with SURMOUNT-5, published in the New England Journal of Medicine in 2025: a 72-week open-label trial in 751 adults with obesity but without diabetes, directly comparing tirzepatide with semaglutide 2.4mg. Tirzepatide produced greater average weight reduction. NICE's appraisal of tirzepatide (TA1026, published December 2024) acknowledged this, noting that indirect comparisons across the SURMOUNT and STEP programmes also favour tirzepatide.
The picture is shifting, though. The 7.2mg maintenance dose of Wegovy (approved by the MHRA in 2026) achieved roughly 20.7% average weight loss over 72 weeks in trials, which narrows the gap considerably. Whether tirzepatide is definitively better than Wegovy is a question that now depends heavily on which Wegovy dose is part of the comparison. The table below summarises the key numbers.
| Factor | Tirzepatide (Mounjaro) | Wegovy (semaglutide injection) |
|---|---|---|
| Mechanism | Dual GIP + GLP-1 receptor agonist | GLP-1 receptor agonist |
| UK weight-management licence | Yes (BMI ≥30, or ≥27 with a weight-related condition) | Yes (BMI ≥30, or ≥27 with a weight-related condition) |
| Average weight loss (pivotal trial) | ~20–21% at 15mg over 72 weeks (SURMOUNT-1, NEJM) | ~15% at 2.4mg over 68 weeks; ~20.7% at 7.2mg over 72 weeks |
| Head-to-head evidence | Greater average loss vs semaglutide 2.4mg (SURMOUNT-5, NEJM 2025) | 7.2mg dose narrows the gap; no head-to-head vs tirzepatide yet |
| NICE recommendation | TA1026 (BMI ≥35 + ≥1 comorbidity for NHS; private criteria differ) | TA875 (specialist services; max 2 years on NHS) |
A question our prescribers hear most weeks: do the side effects differ between the two?
Both medicines share a gastrointestinal side-effect profile, nausea, loose stools, constipation, indigestion and reduced appetite being the most common. These tend to peak after a dose increase and settle within a week or two for most people. Injection-site reactions, fatigue and mild headache are also reported with both. The NHS medicines page for tirzepatide and the equivalent page for semaglutide set out the full lists, and the Patient Information Leaflets that come with your pen are the definitive reference.
Pancreatitis is a serious but infrequent risk with GLP-1 medicines generally: the MHRA issued a Drug Safety Update on this in January 2026, flagging severe stomach pain that spreads to the back as a reason to seek urgent medical help. Both Mounjaro and Wegovy carry Black Triangle (▼) status in the UK, meaning the MHRA monitors new safety information actively. On the contraception side, tirzepatide specifically may reduce absorption of oral contraceptives, the NHS advises adding a non-oral method for the first four weeks of treatment and after each dose increase. There is no equivalent recommendation for semaglutide at present.
Which medicine is available privately, and how does the process work?
Both Mounjaro and Wegovy are available on a private prescription through a regulated UK pharmacy. Neither can be supplied legally without one. If you've looked at the question from the cost angle, why Wegovy has typically been priced lower than Mounjaro relates partly to the dose-escalation path and partly to market dynamics since Eli Lilly's list-price revision in September 2025. Private prices across providers have ranged roughly £149–£375 per month depending on dose and pharmacy, as widely reported.
At nume, the consultation, prescription, delivery and aftercare come in one transparent price, no subscription, no auto-renewal. A named clinician reviews every consultation the same day. If you're considering switching from one to the other, switching from Wegovy to tirzepatide is a clinical decision that depends on your current dose, any side effects you've experienced, and your response so far. Our clinical team reviews every case individually, and if you want to understand what the difference between Mounjaro and Wegovy means in practice, that page sets out the key points before you speak to a prescriber. If you'd like to go deeper on the active ingredients, our tirzepatide versus Ozempic comparison explains how the two compounds compare across mechanism, dosing and evidence. The comparison table above is a starting point, not a prescription. Speak to our prescribers to work through which option fits your health and circumstances.
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