Mounjaro®
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Start journey Learn moreHow a Mounjaro-to-Wegovy Switch Works in Practice, and What the Evidence Says
Step 1: Understand why the switch is being considered
A question our prescribers hear most weeks is whether switching between Mounjaro and Wegovy is straightforward. The honest answer is: it depends on why you're switching, and a prescriber needs to understand that reason before advising on the move.
The two medicines work differently at the receptor level. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, the only medicine of its kind licensed for weight management in the UK. Wegovy (semaglutide) targets a single pathway, the GLP-1 receptor. Both slow gastric emptying, reduce appetite and support weight loss, but their mechanism, titration schedules and side-effect profiles are distinct enough that you cannot simply continue from one to the other as if they were the same drug. A fuller comparison of Wegovy and Mounjaro sets out those differences in detail.
Common reasons people consider a change include gastrointestinal side effects that haven't settled, a supply issue, cost, or a conversation with their prescriber about optimising response. Some people find they tolerate one medicine's GI profile better than the other's. None of these is a self-diagnosis, they're starting points for a clinical conversation.
Step 2: Compare the two medicines before the conversation
Before speaking to a prescriber it helps to understand what you're potentially moving between. The table below summarises the key factual differences, drawing on published trial data and UK regulatory guidance.
| Factor | Mounjaro (tirzepatide) | Wegovy (semaglutide injection) |
|---|---|---|
| Mechanism | Dual GIP + GLP-1 receptor agonist | GLP-1 receptor agonist |
| UK licence | Weight management (BMI ≥30, or ≥27 with a comorbidity) and type 2 diabetes | Weight management (BMI ≥30, or ≥27 with a comorbidity) |
| Average weight loss in trials | Around 20–21% at highest dose over 72 weeks (SURMOUNT-1, NEJM) | Around 15% at 2.4mg over 68 weeks (STEP 1, NEJM); around 20.7% at 7.2mg over 72 weeks |
| Dosing (factual) | Starts 2.5mg weekly; titrated through six strengths up to 15mg | Starts 0.25mg weekly; titrated through five steps up to 2.4mg (or 7.2mg) |
| Head-to-head evidence | Greater average weight reduction than semaglutide 2.4mg in SURMOUNT-5 (NEJM, 2025) | Gap narrows at 7.2mg; no direct head-to-head against tirzepatide at that dose yet |
| Side-effect character | GI-led: nausea, diarrhoea, constipation, reflux, typically most noticeable on dose increases | GI-led: broadly similar profile; individual tolerance varies |
The SURMOUNT-5 trial published in the New England Journal of Medicine (2025) is the only published direct head-to-head comparison; it found tirzepatide produced greater average weight reduction than semaglutide 2.4mg over 72 weeks in adults with obesity and without diabetes. As our Wegovy vs Mounjaro analysis notes, the Wegovy 7.2mg dose narrows that gap, though no head-to-head against it has reported yet. Both medicines carry a Black Triangle (▼) status in the UK, meaning they remain under additional MHRA monitoring, relevant whichever direction you switch. See the NICE appraisal of tirzepatide (TA1026) for the regulatory committee's view of the comparative evidence.
Step 3: The clinical assessment for a switch
Switching is not a matter of stopping one pen on a Monday and starting another on Thursday. A prescriber needs to know: how long you have been on your current medicine, which dose you are taking, whether you've seen a meaningful clinical response, and whether there are any reasons the new medicine might not be suitable. Contraindications, current medications, and your own history all factor in.
At nume, transfer patients provide evidence of their existing treatment as part of the consultation. A GPhC-registered prescriber reads every submission personally (not software) on the day it arrives. Whether switching is right for your situation is a question that deserves a proper clinical answer, not a general rule. The prescriber will also advise on the starting dose for the new medicine; restarting at the lowest tolerated dose is common practice when changing GLP-1 or dual-agonist medicines, but this is a clinical call.
It's also worth noting that some people ask the question in reverse. If you're considering changing from Wegovy back to Mounjaro, the same principle applies: clinical review first, evidence provided, prescriber-led. The practical steps for switching between these medicines are explored more fully in a dedicated guide on this site.
Step 4: Starting the process with a regulated UK prescriber
Both Mounjaro and Wegovy are prescription-only medicines. The only legal route to either in the UK is a prescription issued following a clinical assessment, this is not a formality, it is the safeguard that keeps these medicines safe. If you've seen online sellers offering them without a prior consultation, that is a red flag; the MHRA has warned repeatedly about counterfeit and unlicensed GLP-1 pens circulating in the UK, and some seizures have involved fake pens containing other substances. Check that any pharmacy you use appears on the GPhC register before placing an order.
nume's clinical team can assess whether the switch is appropriate for you, advise on which medicine and starting point fits your history, and, once clinically approved, dispatch treatment the same day. Our clinical team works to one standard: every consultation reviewed by a named prescriber, no exceptions. Cost context for both medicines is covered in detail on our Wegovy vs Mounjaro cost page, a useful read before your consultation. Which medicine suits you is a clinical decision our prescribers make with you.
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