Mounjaro vs Wegovy: what the clinical study evidence tells us

The decision in front of you: two licensed medicines, one clinical choice

Most people searching this topic aren't writing a literature review. They're asking: which one is actually better for me? That's a question our prescribers hear most weeks, and it's worth being direct about what the evidence can and cannot settle.

Both Mounjaro and Wegovy are licensed in the UK for weight management in adults with a BMI of 30 or above, or 27 and above alongside a weight-related condition. Both are once-weekly subcutaneous injections. Both work by slowing gastric emptying and reducing appetite through gut-hormone pathways. Mounjaro activates two receptors (GIP and GLP-1); Wegovy targets the GLP-1 receptor alone. If you want a side-by-side breakdown of how these two medicines compare before your consultation, our Wegovy vs Mounjaro page sets out the key differences clearly.

Our clinical team looks at your health history, any medicines you already take, and your own treatment goals. The study data gives the starting point; the consultation fills in the rest. You can read more about both treatment options before you decide whether to take that step.

What SURMOUNT-5 actually found — and where the numbers come from

SURMOUNT-5 randomised 751 adults with obesity and no diabetes to tirzepatide or semaglutide 2.4mg for 72 weeks. Both groups also followed lifestyle support. Tirzepatide produced greater average body-weight reduction across the trial period. NICE's appraisal of tirzepatide (TA1026) noted that indirect comparisons from the wider evidence base also favour tirzepatide, though direct head-to-head trials had been limited until SURMOUNT-5.

The table below summarises the key trial figures side by side. All figures are population averages from clinical trials; individual results vary.

One important nuance: Wegovy's newer 7.2mg dose, approved by the MHRA in January 2026 with a dedicated single-dose pen approved in April 2026, reported around 20.7% average weight loss over 72 weeks in its supporting trials. That narrows the gap with tirzepatide's highest-dose figures considerably. For more on how the dosing ladders compare, see our page on Wegovy vs Mounjaro dosing.

Where the study evidence has limits

Averages describe populations, not individuals. Someone who responds exceptionally well to semaglutide may lose more weight than the average tirzepatide participant — and vice versa. Trial populations are also carefully selected; real-world results reflect more varied health histories, other medicines, and adherence patterns.

Side-effect profiles matter too, and they differ between individuals rather than between medicines in any predictable way. Both carry a GI-led side-effect profile: nausea, loose stools, constipation, reflux and fatigue are the most commonly reported, typically most noticeable when starting or after a dose increase, then settling over time. For a fuller comparison of how they sit alongside each other in practice, the clinical comparison of Wegovy and Mounjaro covers tolerability, eligibility and prescriber considerations in more depth.

It is also worth noting what this comparison does not include. Ozempic is semaglutide but licensed for type 2 diabetes, not weight management; it should not be confused with Wegovy even though the active ingredient is the same. If you've come across Ozempic in the context of weight loss, the Mounjaro vs Ozempic page explains the licensing distinction clearly.

Which medicine suits you, and how the consultation resolves that

The study data gives a reasonable signal: tirzepatide has shown greater average weight loss at its highest dose in the most direct comparison available. But a number of factors sit outside the trial data entirely, your cardiovascular history, other prescriptions you take, whether injections suit you, and whether you've already tried one treatment without success.

Cost also plays a real part in the decision. Both medicines are private prescriptions at liste prices that have shifted significantly; a transparent comparison of the two is on our Mounjaro vs Wegovy cost in the UK page. For a broader look at the clinical factors involved, the Wegovy or Mounjaro guide covers the decision from a prescriber's perspective.

Which medicine suits you is a clinical decision our prescribers make with you. At nume, a real clinician reviews your consultation the same day and discusses the right option for your situation. Speak to our prescribers to start that conversation, at no cost.