Mounjaro®
Starting from £179.99/mo
Start journey Learn moreWhat the data, the licences and the clinical reality actually tell you
What SURMOUNT-5 showed, and where the comparison gets complicated
The SURMOUNT-5 trial is the clearest comparison available. Over 72 weeks, 751 adults with obesity but without type 2 diabetes were randomised to tirzepatide or semaglutide 2.4mg. Tirzepatide produced meaningfully greater average weight reduction, a result consistent with how the two medicines work. Mounjaro activates two receptors simultaneously (GIP and GLP-1), whereas Wegovy targets GLP-1 alone, and if you are wondering which of the two has the edge on inflammation, that difference in mechanism is central to the answer. The NICE appraisal of tirzepatide (TA1026) noted that indirect comparisons also favour tirzepatide, making the head-to-head result less surprising in hindsight.
However, the picture shifted slightly in early 2026. The MHRA approved a higher Wegovy maintenance dose of 7.2mg, and trials at that dose showed around 20.7% average weight loss over 72 weeks, approaching results seen at tirzepatide's highest strength. For someone who has switched from Wegovy to Mounjaro and found the side effects harder to tolerate, or for whom tirzepatide is contraindicated, the 7.2mg semaglutide option may now matter. The MHRA's approval of the dedicated 7.2mg single-dose pen was confirmed on 14 April 2026. Availability at any given dose should be confirmed at consultation.
None of this means one medicine is universally superior. It means the numbers are closer than they once appeared, and the right choice depends on clinical detail rather than a league table.
Side-effect profiles: what people notice after switching
A question our prescribers hear most weeks is whether switching medicines will reset the side-effect experience. The short answer: partly, yes, because you move back down a titration ladder, and both medicines share a predominantly gastrointestinal side-effect profile. Nausea, constipation, diarrhoea, indigestion and fatigue are common to both, as documented on the NHS tirzepatide page and its semaglutide equivalent. Symptoms tend to be most noticeable when starting or increasing a dose, and often settle within a couple of weeks.
What some people report after switching is a different pattern of symptoms rather than an absence of them. There is no published direct comparison of side-effect burden at equivalent weight-loss efficacy doses, so individual experience varies. People who have switched and found themselves feeling hungrier than expected are responding to a real pharmacological difference: the dual GIP/GLP-1 action of tirzepatide affects appetite signalling through two pathways, and moving to a single-pathway medicine can feel different, particularly during the re-titration period.
Anyone experiencing severe, persistent abdominal pain that spreads to the back should seek urgent medical attention. The MHRA highlighted acute pancreatitis as an infrequent but serious risk associated with GLP-1 medicines in a January 2026 Drug Safety Update.
How the two medicines compare on key clinical facts
| Factor | Mounjaro (tirzepatide) | Wegovy injection (semaglutide) |
|---|---|---|
| Mechanism | Dual GIP and GLP-1 receptor agonist | GLP-1 receptor agonist |
| 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); ~20.7% at 7.2mg over 72 weeks |
| UK-licensed maintenance doses | Up to 15mg once weekly | Up to 7.2mg once weekly |
| NICE recommendation | TA1026: BMI ≥35 plus ≥1 comorbidity (or lower thresholds for some ethnic backgrounds) | TA875: BMI ≥35 plus ≥1 comorbidity, within specialist services, max 2 years |
| Common side effects | GI-led: nausea, constipation, diarrhoea, fatigue | GI-led: nausea, constipation, diarrhoea, fatigue |
| Injection frequency | Once weekly | Once weekly |
For a fuller breakdown of how costs sit alongside these differences, the Wegovy vs Mounjaro cost comparison covers that ground in detail.
Making the switch: what the process actually involves
Switching is not a simple swap. Whether you are moving from Mounjaro to Wegovy or considering the reverse direction, a prescriber needs to understand why: supply disruption, tolerability, efficacy plateau, or a clinical reason. They also need to know your current dose, your recent weight, and any conditions that have changed since you started treatment.
At nume, every switch request is handled as a fresh clinical consultation. There is no auto-renewal, and no dose is assumed, the prescriber makes an independent decision based on the information you provide. That process exists because the same clinical rigour that governs starting treatment also applies when changing it.
If you are mid-titration on either medicine, your prescriber will advise on where re-titration should begin on the new agent; this is not something to determine from a webpage. The Patient Information Leaflet for each medicine contains the manufacturer's guidance, and your prescriber can explain what that means for your specific situation. People with particular questions about individual experience after switching can also read accounts of what others have found, though their experience will not predict yours.
The broader Mounjaro vs Wegovy picture is covered on the dedicated comparison page. Which medicine suits your biology, history and goals is the kind of question our prescribers are well-placed to work through with you.
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