Mounjaro®
Starting from £179.99/mo
Start journey Learn moreHow the evidence shapes a switch from 1mg Wegovy to Mounjaro
What the trial data shows about these two medicines side by side
The place to start is the evidence, because the numbers are the clearest guide to what a switch might mean in practice. In the STEP 1 trial, published in the New England Journal of Medicine, adults taking semaglutide 2.4mg weekly lost around 15% of their body weight on average over 68 weeks. That is the full maintenance dose of Wegovy; 1mg sits partway through the titration schedule and is not a maintenance dose, so it would not be expected to produce results close to those headline figures.
Mounjaro's phase-3 SURMOUNT-1 trial, also published in the NEJM, reported average body-weight reductions of around 20 to 21% at the 15mg dose over 72 weeks. The SURMOUNT-5 head-to-head study (published in the New England Journal of Medicine in 2025) compared tirzepatide directly with semaglutide 2.4mg in adults with obesity and no diabetes; tirzepatide produced greater average weight reduction. NICE's appraisal of tirzepatide (TA1026) acknowledges this advantage, noting that indirect comparisons favour tirzepatide.
What this means for someone at 1mg Wegovy is straightforward to frame but less easy to quantify precisely: 1mg is roughly the dose you pass through in the first four weeks of Wegovy treatment. Moving to Mounjaro at that point means starting a new titration from Mounjaro's 2.5mg starter dose, not slotting into a clinical equivalent of where you are on Wegovy. The concept of what 1mg Wegovy is in Mounjaro terms is explored in more detail on our page covering 1mg Wegovy equivalent to Mounjaro.
Why there is no direct dose conversion between 1mg Wegovy and Mounjaro
A question our prescribers hear most weeks is whether 1mg of Wegovy corresponds to a particular Mounjaro dose — 5mg, perhaps, or somewhere in the middle of the range. The honest answer is that no such correspondence exists in the clinical literature.
The two medicines activate different receptors. Semaglutide targets GLP-1 receptors only. Tirzepatide is the only dual GIP and GLP-1 receptor agonist licensed for weight management in the UK, meaning it activates two separate signalling pathways simultaneously. That biological difference makes a straight milligram comparison meaningless: the dose ladders were built for each drug's own pharmacology, not as translations of each other. Wegovy's titration runs from 0.25mg up to 2.4mg; Mounjaro's runs from 2.5mg up to 15mg. The numbers overlap but the mechanisms do not.
When someone switches, the standard clinical approach is to begin Mounjaro at the 2.5mg starter dose regardless of which Wegovy dose they were on, unless there is a clinical reason to consider otherwise. Our page on dose conversion between Mounjaro and Wegovy covers the broader switching picture, including moves in both directions. For the specific question of how 1mg compares to individual Mounjaro doses, our page comparing Wegovy 1mg and Mounjaro 5mg and 1mg Wegovy versus Mounjaro 7.5mg look at those individual matchups in detail.
Key differences at a glance
| Factor | Wegovy (semaglutide) | Mounjaro (tirzepatide) |
|---|---|---|
| Receptor pathway | GLP-1 agonist only | Dual GIP and GLP-1 agonist |
| UK dose range | 0.25mg to 2.4mg weekly (7.2mg also approved) | 2.5mg to 15mg weekly |
| Average weight loss at maintenance (clinical trials) | ~15% at 2.4mg (STEP 1, NEJM) | ~20–21% at 15mg (SURMOUNT-1, NEJM) |
| Head-to-head evidence | Lower average loss vs tirzepatide (SURMOUNT-5, 2025) | Greater average loss vs semaglutide 2.4mg (SURMOUNT-5, 2025) |
| NICE recommendation | TA875 (within specialist weight management services, max 2 years | TA1026) BMI ≥35 plus one or more weight-related conditions |
| Administration | Once-weekly injection; 7.2mg oral option also available | Once-weekly injection via KwikPen |
Numbers in the table above come from NICE TA1026 and the published STEP 1 and SURMOUNT-1 trial papers. Individual results will vary; trial participants followed a reduced-calorie diet and increased activity alongside treatment.
What a switch actually involves at a service like ours
Switching from Wegovy to Mounjaro is not a self-managed process. Because both are prescription-only medicines, each change requires a new prescription issued by a qualified prescriber after a clinical review of your current treatment, dose history and any side effects you have experienced.
At nume, transfer patients are asked to provide evidence of their current treatment before a new prescription is considered. That evidence review, along with the wider clinical picture, is assessed the same day by one of our GPhC-registered Independent Prescribers. There is no algorithm making that call. You can read more about how our clinical team approaches these decisions on the clinical team page, or explore the full treatment options available through our weight-loss treatments overview.
A broader comparison of how Wegovy and Mounjaro sit alongside each other, covering cost context as well as clinical evidence, is on our Wegovy versus Mounjaro page. If pricing is part of your thinking, the Mounjaro and Wegovy price comparison page sets out what the cost difference looks like in practice. Which medicine suits you is a clinical decision our prescribers make with you, not something a comparison table can settle on your behalf.
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