Mounjaro®
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Start journey Learn moreThe factors that shape whether (and how) a prescriber would approve a switch
Why someone might want to switch, and why the pathway matters
People consider moving from Mounjaro to Wegovy (or the reverse) for practical reasons: supply issues at a particular strength, tolerability differences, cost, or simply wanting to try a different medicine after results have plateaued. All of those are legitimate starting points for a conversation with a prescriber. What they are not, by themselves, is a reason to make the change independently.
Mounjaro (tirzepatide) activates two gut-hormone receptors (GIP and GLP-1) while Wegovy (semaglutide) targets the GLP-1 receptor alone. Switching is therefore not like swapping a branded medicine for its generic equivalent; you are moving between two pharmacologically distinct medicines, each with its own titration schedule and its own side-effect profile. The full clinical comparison of Wegovy and Mounjaro sets out those differences in detail. The transition itself carries the main risk: getting the timing wrong or misjudging the equivalent dose can mean either an abrupt drop in coverage (leading to rapid hunger return) or an overshoot that amplifies gastrointestinal side effects. A prescriber who reviews your weight history, your current dose, and the reason for switching can plan the crossover to avoid both.
If you're reading this after finding a provider willing to change your prescription without asking those questions, that is worth pausing on.
What the clinical evidence says about the two medicines side by side
Choosing which medicine suits a person better is a clinical judgement; the trial data gives context but not a universal answer. The table below summarises the key comparable facts.
| Factor | Mounjaro (tirzepatide) | Wegovy (semaglutide) |
|---|---|---|
| Receptor mechanism | Dual GIP + GLP-1 agonist | GLP-1 agonist |
| Average weight reduction in pivotal trial | ~20–21% at 15 mg over 72 weeks (SURMOUNT-1, NEJM) | ~15% at 2.4 mg over 68 weeks (STEP 1, NEJM) |
| Head-to-head comparison | Greater average weight loss in SURMOUNT-5 (72 weeks, 2025) | Narrowed by 7.2 mg dose (MHRA-approved April 2026) |
| Starting dose / schedule | 2.5 mg, titrated by prescriber typically in 4-week steps | 0.25 mg, titrated by prescriber approximately every 4 weeks |
| UK licence (weight management) | BMI ≥30, or ≥27 with ≥1 weight-related condition | BMI ≥30, or ≥27 with ≥1 weight-related condition |
| Common side effects | GI-led: nausea, diarrhoea, constipation, reflux | GI-led: nausea, vomiting, diarrhoea, constipation |
Numbers from SURMOUNT-1 (tirzepatide) and STEP 1 (semaglutide 2.4 mg), both published in the New England Journal of Medicine; SURMOUNT-5 results published in NEJM 2025. The side-effect comparison between Wegovy and Mounjaro goes deeper on tolerability differences if that's the main driver of your decision.
The safety considerations specific to switching
It's completely understandable to feel uncertain here, switching medicines mid-treatment is genuinely less straightforward than starting fresh, and the questions patients bring to this decision are reasonable ones.
The side-effect picture during a switch deserves particular attention. Both medicines slow the stomach, so moving from one to the other can mean a temporary spike in gastrointestinal symptoms as your system adjusts to a different receptor profile. If you want to know what to expect before you commit, our page covering what side effects to anticipate when switching from Mounjaro to Wegovy walks through what patients commonly report at each stage of the transition. You can also read about the side effects people experience when moving from Mounjaro to Wegovy, including how symptoms tend to change as the new medicine takes hold. The NHS medicines page for tirzepatide and the equivalent page for semaglutide both list what to monitor and when to seek urgent help.
Pancreatitis is a known but infrequent serious risk with this class of medicine, the MHRA issued a Drug Safety Update on this in January 2026. Severe or persistent stomach pain that spreads to the back, with or without vomiting, needs prompt medical attention regardless of which medicine you're taking, but it is especially important to flag during a transition period when symptoms can otherwise be dismissed as expected adjustment.
On contraception: if you are switching to Mounjaro and use oral contraceptives, you'll need to add a barrier method for the first four weeks of treatment and for four weeks after each dose increase, because tirzepatide can reduce pill absorption. That's a detail prescribers often cover at initiation but that can get missed in a mid-treatment switch, the safety comparison of Mounjaro and Wegovy covers this and related interactions in full.
How a prescriber would approach the decision, and how to check your eligibility with us
A clinician reviewing a switch request will want to know: what dose you're currently on, whether you've completed the recommended period at that dose, your recent weight trajectory, the reason for the switch, and any conditions or medicines that might affect how the new treatment is absorbed or tolerated. Transfer patients at nume provide evidence of their current treatment; dose-level decisions are made on that basis, not assumed.
The cost comparison between Wegovy and Mounjaro is sometimes part of the conversation too, particularly if affordability is what's prompting the move. Our clinical team can discuss that context alongside the clinical picture. If you'd like to understand your options properly, start your free consultation, a real prescriber reviews it the same day. Which medicine suits you, and whether a switch is the right call at all, is a clinical decision made with you, not for you.
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