Mounjaro®
Starting from £179.99/mo
Start journey Learn moreWhat the evidence says about switching, and how a prescriber approaches the decision
The misconception: 0.5mg Wegovy and 2.5mg Mounjaro are roughly equivalent starting points
A question our prescribers hear most weeks is whether 0.5mg Wegovy is roughly the same as 2.5mg Mounjaro, because both are early-titration doses. They're not the same thing, and treating them as interchangeable is the most common misunderstanding about this switch.
Wegovy (semaglutide) and Mounjaro (tirzepatide) activate different receptors. Semaglutide targets the GLP-1 receptor only. Tirzepatide is the UK's only dual GIP and GLP-1 receptor agonist, meaning it engages two gut-hormone pathways involved in appetite and blood-sugar regulation. The starting doses exist for the same reason in both cases: to let your body adjust and reduce the risk of nausea, not because lower doses are where the clinical effect is strongest. But because the molecules are structurally different, there is no validated milligram-for-milligram conversion between them. The dose conversion page explains this in more detail, but the short version is: no published conversion table can reliably map 0.5mg semaglutide onto a tirzepatide dose. A prescriber assesses the switch on its own terms.
If you've been on 0.5mg Wegovy for fewer than four weeks, you're still in the early tolerability phase. A switch now would mean starting Mounjaro's own titration from 2.5mg and going through the adjustment period again. That's sometimes the right call, but it's a clinical decision, not a like-for-like swap.
How 0.5mg Wegovy and Mounjaro's early doses compare on the evidence we have
The table below sets out the key factual differences. Numbers from trials reflect averages at each medicine's highest maintenance dose, not at the doses being compared here, which is worth stating plainly.
| Factor | Wegovy (semaglutide) | Mounjaro (tirzepatide) |
|---|---|---|
| Receptor target | GLP-1 only | GIP + GLP-1 (dual) |
| Starting dose | 0.25mg weekly | 2.5mg weekly |
| 0.5mg in the schedule | Second step (weeks 5–8 typically) | Not a Mounjaro dose strength |
| Average weight loss at highest maintenance dose (trial data) | ~15% over 68 weeks at 2.4mg [STEP 1, NEJM] | ~20–21% over 72 weeks at 15mg [SURMOUNT-1, NEJM] |
| Head-to-head evidence | SURMOUNT-5 (NEJM, 2025): tirzepatide produced greater average weight reduction than semaglutide 2.4mg over 72 weeks in adults with obesity | |
| UK licence | Weight management, BMI ≥30 or ≥27 with a weight-related condition | Weight management and type 2 diabetes, same BMI thresholds |
The SURMOUNT-5 comparison is the closest thing to a head-to-head we have for these two medicines, and it favoured tirzepatide at full maintenance doses. What it cannot tell you is how a switch at the 0.5mg Wegovy stage will play out for any individual. The detailed dose-level comparison unpacks the trial data further if you want to go deeper on the numbers.
What a switch actually involves, practically
Switching from Wegovy to Mounjaro isn't a matter of receiving a different pen in next month's delivery. It is a clinical reassessment. At nume, that means a prescriber reviews your current dose, how long you've been on it, your response so far, any side effects, your full health picture and whether tirzepatide is appropriate for you. Evidence of your current treatment is part of that process.
Mounjaro is dispensed as a pre-filled KwikPen, one pen covering four weekly doses. Wegovy is a separate pen format. Storage for both requires refrigeration at 2–8°C; for exact room-temperature handling windows, the patient information leaflet and the medicine's SmPC on the eMC are the definitive references, not this page.
On the question of cost, private treatment prices differ between the two medicines. The Mounjaro and Wegovy price comparison covers what's typically included and what varies between providers. At nume, one price covers everything: the clinical assessment, prescription, medicine and delivery. Current pricing is shown on the treatment page rather than here, because prices can move and body copy shouldn't lag behind.
For anyone already established on a higher Wegovy dose who's weighing a switch, the considerations shift again. The 7.5mg Mounjaro to Wegovy comparison and the 5mg Mounjaro equivalent page cover those positions specifically.
Which suits you is a clinical decision, not a comparison-page verdict
No comparison table, however thorough, can substitute for a prescriber who has reviewed your notes. Both medicines are licensed for the same broad population in the UK, per NICE's appraisal of tirzepatide (TA1026) and NICE's recommendation for semaglutide (TA875). Both have GI-led side-effect profiles. Both require clinical oversight at every stage. The question isn't which is better in the abstract; it's which is right for you right now, given where you are in treatment.
That's exactly the kind of question our prescribers work through. If you want to explore whether switching is appropriate, start a free consultation and your case lands on a real clinician's desk the same day. You can also read more about how we approach these decisions on the about us page or review our clinical team's credentials via our clinical lead's profile.
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