Does Wegovy Work the Same Way as Mounjaro?

The biggest misconception: that these are just different brands of the same thing

A common assumption is that Wegovy and Mounjaro are interchangeable, two brands competing for the same slot, like own-brand versus supermarket paracetamol. That's not accurate. Both belong to the GLP-1 class and both slow gastric emptying, reduce appetite and help regulate blood sugar, but the underlying mechanism differs in a way that matters clinically.

Wegovy contains semaglutide, a GLP-1 receptor agonist. It mimics one gut hormone. Mounjaro contains tirzepatide, which is a dual GIP and GLP-1 receptor agonist, the only weight-loss medicine licensed in the UK that works on both pathways simultaneously. The addition of the GIP pathway appears to amplify the appetite-suppressing and metabolic effects beyond what a single-pathway medicine achieves. This is not a marginal tweak; it is a structurally different approach, reflected in the trial data. You can read more about the distinction in detail on our comparison of what Wegovy and Mounjaro actually share.

Both medicines are licensed in the UK for weight management in adults, both are prescription-only, and both require clinical assessment before a prescriber can recommend one. Neither is a shortcut.

What the trial evidence shows, and how to read it honestly

The STEP 1 trial, published in the New England Journal of Medicine, found that semaglutide 2.4mg (Wegovy) produced an average body-weight reduction of around 15% over 68 weeks alongside lifestyle changes. That is a meaningful result; it changed how clinicians think about medical weight management. SURMOUNT-1, the comparable trial for tirzepatide, reported average reductions of around 20–21% at the 15mg dose over 72 weeks, and a head-to-head study matters even more here.

In the SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, tirzepatide produced greater average weight loss than semaglutide 2.4mg in adults with obesity and no diabetes, over 72 weeks. NICE cited indirect comparisons favouring tirzepatide when issuing its appraisal of tirzepatide (NICE TA1026). It is worth noting that Wegovy's newer 7.2mg dose, approved by the MHRA in 2026, narrows that gap, trials reported around 20.7% average weight loss at 7.2mg, approaching tirzepatide 15mg results. If you want a closer look at how well Wegovy performs compared to Mounjaro across these figures, we cover that question in detail separately.

Numbers like these are averages across populations. Individual response varies considerably, and what a trial participant achieves is not a prediction of what you will achieve. A comparison of results across both medicines is set out in the table below.

Side-effect profiles are broadly similar: gastrointestinal symptoms dominate for both, typically most noticeable at the start of treatment or after a dose increase, then settling for most people. The NHS medicines page for tirzepatide and its semaglutide equivalent set out the full lists clearly.

Practical differences worth knowing before your consultation

Beyond the mechanism and the numbers, there are a few practical contrasts that often come up. Tirzepatide (Mounjaro) uses a pre-filled KwikPen delivering four weekly doses per pen; semaglutide (Wegovy) uses a different pre-filled pen format. Both are subcutaneous injections, rotated between the abdomen, thigh and upper arm. Storage for both requires refrigeration, with a limited room-temperature window detailed in each medicine's Patient Information Leaflet, the exact window differs, so the leaflet is the right place to check, not a comparison article.

On eligibility, both medicines share the same licensed BMI thresholds. NHS access is a different matter: tirzepatide is being phased into the NHS under NICE TA1026, with strict comorbidity criteria, while Wegovy is available through specialist NHS weight management services under NICE TA875. Private treatment through a regulated pharmacy like our pharmacy offers a faster route for people who are clinically suitable but cannot access NHS provision or prefer not to wait. The question of which medicine is more cost-effective privately is explored separately on our cost comparison page.

The contraception consideration also differs between the two: for tirzepatide specifically, women taking the oral contraceptive pill are advised to use an additional non-oral method for the first four weeks of treatment and for four weeks after each dose increase, because absorption of the pill may be reduced. The NHS does not flag an equivalent concern for semaglutide. This is worth raising with a prescriber, not deciding alone, and our prescribers are used to these conversations.

For a fuller look at how the two medicines sit alongside each other across every dimension, the Wegovy vs Mounjaro page covers the topic in detail. If your interest is specifically in whether switching from one to the other makes sense, what happens when you move from Mounjaro to Wegovy is a question our prescribers address at consultation, and our page on whether Wegovy works as well as Mounjaro explores the evidence behind that decision in more depth. The answer depends on your history, your current dose and your clinical goals, not a general rule.

Which of these two medicines suits you is a clinical decision our prescribers make with you. Speak to our prescribers, your consultation is free, and a named clinician reviews it the same day.