Mounjaro®
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Start journey Learn moreWhat the trial data and UK guidance tell us about switching between these two medicines
How Mounjaro and Wegovy differ — and why that gap matters when switching
The most direct clinical comparison we have is the SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025. In that 72-week head-to-head study involving 751 adults with obesity and no diabetes, tirzepatide (Mounjaro) produced greater average weight reduction than semaglutide 2.4mg (Wegovy). NICE's appraisal of tirzepatide, TA1026, notes that indirect comparisons across the trial programmes similarly favour tirzepatide at comparable doses.
The mechanism explains part of that gap. Mounjaro activates two gut-hormone receptors, GIP and GLP-1. Wegovy targets GLP-1 alone. Both slow gastric emptying and reduce appetite, but the dual action of tirzepatide appears to produce stronger average results in the evidence to date.
That said, individual responses vary considerably, and Wegovy is not a lesser medicine. The STEP 1 trial, published in the New England Journal of Medicine, reported around 15% average body-weight reduction over 68 weeks at 2.4mg, meaningful outcomes for most participants. And the newer 7.2mg Wegovy dose, approved by the MHRA in April 2026, narrows the gap further, with trial data reporting roughly 20.7% average weight loss over 72 weeks. If you're curious how the mechanisms diverge at a molecular level, our page on Mounjaro vs Wegovy mechanism of action covers that in more depth.
When switching from Mounjaro to Wegovy might be the right clinical call
There are genuine reasons a prescriber might recommend moving from tirzepatide to semaglutide. Tolerability is the most common. Some people find the GI side-effect profile of Mounjaro harder to manage, nausea, vomiting, or reflux that doesn't settle in the way it does for most patients. Semaglutide has a broadly similar GI profile but the intensity differs for some individuals, and switching may improve day-to-day comfort while maintaining meaningful weight loss.
Supply availability occasionally factors in too. If a particular Mounjaro dose has been temporarily constrained, a prescriber might discuss Wegovy as a bridge rather than interrupting treatment entirely. Cost context can also shift over time. Following Eli Lilly's list price increase in September 2025, Mounjaro's highest doses rose sharply (as widely reported) and some patients explore whether Wegovy at an equivalent stage of treatment offers comparable results at a different price point. The cost comparison between Wegovy and Mounjaro is a reasonable question, though price should never be the only factor for a prescription medicine.
On the other side of the question, patients who want to know whether they can switch from Mounjaro to Wegovy will find the logic works in both directions. Someone who has plateaued on Wegovy, or who simply hasn't responded as hoped, may be a candidate for tirzepatide's dual-receptor approach, subject to prescriber assessment.
What the switch actually involves in practice
Switching isn't a straight dose-for-dose swap, and this is where clinical oversight matters most. Tirzepatide and semaglutide are different molecules with different dose scales. A prescriber needs to assess what dose you've been stable on, how long you've been at that level, what your current weight trajectory looks like, and whether any side effects influenced the decision to switch.
There's also the wash-out question. Because both medicines affect gastric motility, starting a new one too quickly after stopping the last can compound side-effect risk. A prescriber will advise on timing, and timing matters practically too. If you're planning a switch, our guide to switching from Mounjaro to Wegovy explains what to expect at each stage, and factoring it around something straightforward (a regular weekly order window, not the week of a holiday abroad) makes the process smoother.
Contraception is worth flagging explicitly at this point: women taking oral contraceptives should add a barrier method for the first four weeks on tirzepatide and for four weeks after each dose increase, because absorption of the pill may be reduced. The equivalent guidance for Wegovy does not apply in the same way, so switching direction matters here. NHS England's guidance on weight-management injections covers this alongside HRT and surgery considerations.
For a broader grounding in how these two medicines compare on efficacy, side effects, and eligibility, our Wegovy vs Mounjaro overview sets it all out clearly.
Side by side: key facts for switching decisions
| Factor | Mounjaro (tirzepatide) | Wegovy (semaglutide injection) |
|---|---|---|
| Receptor action | Dual GIP + GLP-1 agonist | GLP-1 agonist |
| Average weight loss in trials | ~20–21% at 15mg (SURMOUNT-1); greater than semaglutide 2.4mg in SURMOUNT-5 head-to-head | ~15% at 2.4mg (STEP 1); ~20.7% at 7.2mg in trials |
| UK licensed doses | 2.5mg to 15mg (six strengths) | 0.25mg to 2.4mg standard; 7.2mg approved April 2026 |
| Starting dose | 2.5mg (tolerability/starter) | 0.25mg |
| Oral contraceptive interaction | Add barrier method for 4 weeks on starting and after each dose increase | No equivalent NHS guidance for semaglutide |
| NICE recommendation | TA1026 (Dec 2024); BMI ≥35 + ≥1 comorbidity for NHS access | TA875 (Mar 2023); specialist services, max 2 years, BMI ≥35 + comorbidity |
Sources: NICE TA1026; NICE TA875; SURMOUNT-5, NEJM 2025; STEP 1, NEJM 2021.
Which of these medicines suits you (and whether switching direction makes sense) is a clinical decision our prescribers make with you, based on your individual response and circumstances. If you'd like to discuss a potential switch from Mounjaro to Wegovy, starting a free consultation is the right first step. Our clinical team reviews every case personally.
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