Mounjaro v Wegovy for Weight Loss: What the Trials Actually Found

What the SURMOUNT-5 trial and earlier data actually show

The clearest comparison we have comes from SURMOUNT-5, a head-to-head trial published in the New England Journal of Medicine in 2025. Over 72 weeks, 751 adults with obesity and no diabetes were randomised to either tirzepatide or semaglutide 2.4mg. Tirzepatide produced meaningfully greater average weight reduction. Earlier individual trials had already hinted at this gap: SURMOUNT-1 reported around 20–21% average body-weight loss at the 15mg tirzepatide dose, while STEP 1 found roughly 15% average loss with semaglutide 2.4mg over a similar period. NICE reviewed this evidence when appraising tirzepatide and noted that indirect comparisons favour tirzepatide, though it acknowledged the limitations of cross-trial comparison before SURMOUNT-5 reported. None of these figures are a promise of what any individual will achieve, trial averages include people who responded strongly and people who responded less so. If you are asking whether Wegovy is as good as Mounjaro for weight loss, the answer depends on which trial data you look at and how the two medicines are compared, and our dedicated page works through that question in detail. For a more detailed look at how the percentage reductions stack up, including a thorough breakdown of Wegovy versus Mounjaro across the key trials, the semaglutide vs tirzepatide weight loss percentage breakdown goes through the numbers trial by trial.

One important development for Wegovy: in April 2026 the MHRA approved a higher 7.2mg maintenance dose, with trials reporting around 20.7% average loss over 72 weeks at that dose. That narrows the gap with tirzepatide's top dose considerably. Specific dose availability is confirmed at consultation, not assumed in advance.

How the two medicines work differently

The mechanism difference is real and clinically relevant. Wegovy (semaglutide) is a GLP-1 receptor agonist, it mimics a gut hormone that signals fullness, slows gastric emptying and reduces appetite. Mounjaro (tirzepatide) does that too, but also activates the GIP receptor, a second gut-hormone pathway involved in both appetite regulation and blood-glucose control. It is the only dual-agonist weight-loss medicine licensed in the UK, which partly explains why the trial results have been larger on average. The NHS medicines page on tirzepatide and the equivalent semaglutide page both explain the mechanism clearly if you want a plain-English starting point. What this means practically is that the two medicines have overlapping but not identical profiles, a prescriber's assessment of which fits your individual situation matters more than a headline trial number.

Side-effect profiles are broadly similar: nausea, vomiting, constipation and other gastrointestinal effects are most common for both, typically most noticeable when starting or after a dose increase, and often settling within a couple of weeks. Both carry a Black Triangle (▼) designation, meaning they are under additional MHRA monitoring. Pancreatitis is a known but infrequent risk with GLP-1 class medicines generally, severe, persistent stomach pain that reaches the back is a reason to seek urgent medical attention.

A quick comparison of the key facts

Both are prescription-only medicines. NICE TA1026 recommends tirzepatide for adults with a BMI of 35 or above and at least one weight-related comorbidity (lower thresholds apply for some ethnic backgrounds). NICE TA875 covers semaglutide but with stricter NHS conditions, a specialist service, a maximum treatment duration of two years, and multidisciplinary support. Our Wegovy vs Mounjaro comparison page covers the cost picture alongside the clinical differences, which adds another layer worth understanding before deciding.

Which one is right for you, and how a prescriber decides

There is no universal answer here, which is exactly why these medicines require clinical assessment. A prescriber will look at your BMI, your medical history (including whether you have type 2 diabetes, cardiovascular risk factors or previous GI conditions), any medicines you currently take, and your preferences around injection technique and titration pace. Oral contraceptive users, for example, are advised to add a non-oral method of contraception for the first four weeks of tirzepatide treatment and after each dose increase, because the pill's absorption can be affected, the equivalent evidence does not exist for semaglutide. That is a small but genuinely useful clinical distinction. For a deeper read on effectiveness factors, the is Wegovy as effective as Mounjaro page works through the nuances in more detail.

Some people have tried one medicine and want to understand what switching might involve. Others are approaching this for the first time and feel pulled between the trial numbers and the practicalities. A question our prescribers hear regularly is simply: 'Which should I start with?' The honest answer is that it varies, and a Monday order placed before noon, once approved, goes out the same day, so there is no practical reason to delay getting a clinical view. Our prescribers work through this with you, one consultation at a time. See how Mounjaro and Wegovy compare on weight loss if you want a fuller breakdown before starting, or start your free consultation when you are ready for a prescriber to make that assessment with you. You can also read about how nume works or explore our weight-loss treatment options more broadly.