Mounjaro®
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Start journey Learn moreHow Mounjaro and semaglutide compare across the details that matter most
The biggest misconception: semaglutide and Mounjaro are basically the same drug
This is the comparison's most persistent myth, and it's worth correcting first. Both medicines slow gastric emptying and reduce appetite, but that's where the overlap ends. Semaglutide (Wegovy) activates only the GLP-1 receptor. Mounjaro (tirzepatide) activates both the GLP-1 and GIP receptors simultaneously, making it the only dual-agonist weight-loss medicine licensed in the UK. The GIP pathway appears to add meaningful extra effect on appetite regulation and fat metabolism, which is why the two medicines produce different average outcomes even at their respective maximum doses.
It's also worth being clear about brand names, since searches on this topic can get confusing. Wegovy is the semaglutide product licensed for weight management; Ozempic is also semaglutide, but it holds a licence only for type 2 diabetes, not weight loss, and should never be sought for that purpose. Mounjaro is the only tirzepatide brand available in the UK. A closer look at tirzepatide versus semaglutide for weight loss covers the mechanism in more depth if you want the pharmacology unpacked further.
The practical consequence of the mechanism difference shows up in the trials. That distinction matters when you're weighing your options, because the two medicines are not interchangeable, they're genuinely different treatments, and our full Mounjaro versus Wegovy comparison explores what those differences mean in practice.
What the trial results actually say, side by side
The table below draws on published trial data and NICE's appraisal of both medicines. Numbers describe averages across trial populations; individual results vary and depend on dose, duration, diet, activity and other factors.
| Factor | Mounjaro (tirzepatide) | Wegovy (semaglutide) |
|---|---|---|
| Receptor target | GLP-1 and GIP (dual) | GLP-1 only |
| Average weight loss in pivotal trial | ~20–21% at 15mg over 72 weeks (SURMOUNT-1, NEJM) | ~15% at 2.4mg over 68 weeks (STEP 1, NEJM) |
| Head-to-head comparison | Greater average reduction vs semaglutide 2.4mg (SURMOUNT-5, NEJM 2025) | Semaglutide 2.4mg, comparison arm in SURMOUNT-5 |
| Higher-dose option (UK-approved) | Up to 15mg weekly | Up to 7.2mg weekly (single-dose pen approved April 2026); trials report ~20.7% average loss at 7.2mg |
| NICE recommendation threshold | BMI ≥35 plus ≥1 weight-related comorbidity (TA1026) | BMI ≥35 plus ≥1 comorbidity, max 2 years, specialist service (TA875) |
| Administration | Once-weekly subcutaneous injection (KwikPen) | Once-weekly subcutaneous injection or, from June 2026, a once-daily tablet (Wegovy tablets) |
The NICE appraisal of tirzepatide (TA1026) and the NICE appraisal of semaglutide (TA875) set out the evidence committee's conclusions in full if you want the source documents. It's worth noting that Wegovy's 7.2mg dose narrows the gap with tirzepatide's top dose, this comparison is evolving as higher-dose data mature.
Side effects and tolerability: more similar than different
Both medicines share a broadly GI-led side-effect profile because slowing gastric emptying is central to both. Nausea, constipation, diarrhoea, indigestion and occasional vomiting are the most commonly reported effects with each, and both tend to be most noticeable after a new dose is introduced, usually easing over the following days to couple of weeks.
There are some practical differences worth knowing. For women using oral contraceptives, Mounjaro carries a specific interaction caution: because absorption of the pill can be reduced, an additional non-oral contraceptive method (such as condoms) is recommended for the first four weeks of Mounjaro treatment and for four weeks after each dose increase. NHS England's guidance on weight-management injections covers this alongside HRT considerations, which follow similar logic for tirzepatide. No equivalent pill-absorption warning applies to semaglutide at present.
Both medicines carry a Black Triangle (▼) designation in the UK, meaning the MHRA continues to gather safety data. Suspected side effects from either can be reported at the MHRA Yellow Card service. Anyone experiencing severe, persistent abdominal pain should seek medical help promptly, this applies equally to both treatments. The safety comparison between Wegovy and Mounjaro covers the tolerability picture in more detail.
Choosing between them: what actually determines the answer
Raw trial averages are useful context, but they don't settle which medicine is right for any one person. Your prescriber looks at your full medical history, current medications, any relevant conditions and your personal preferences, the outcome number in a trial population is a starting point, not a prescription.
Cost is another real-world factor. Since Eli Lilly raised Mounjaro's UK list price in September 2025, private prices for both medicines vary by dose and provider, typically ranging roughly £149–£375 per month, how the two medicines compare on price is covered separately if that's your main question. Neither is the right choice on price alone; a small cost difference is not the right test for a prescription medicine.
Some people ask about switching between Mounjaro and Wegovy if one stops working or becomes unavailable. That's a clinical conversation, not a self-managed change. At nume, each prescription is reviewed by a named prescriber before it's issued, the kind of individual assessment that a side-by-side comparison page like this one can inform but never replace. If you'd like to explore your options, start a free consultation and one of our prescribers will work through it with you.
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