Mounjaro and Wegovy: what's the difference, and does it matter for you?

You're comparing two medicines that look similar on the surface — here's where they actually diverge

Picture this: you've read that both Mounjaro and Wegovy are weekly injections for weight loss, both come in pre-filled pens, both cause similar side effects, and both sit behind a prescription. So why does the choice matter?

Mounjaro contains tirzepatide, made by Eli Lilly. It's a dual GIP and GLP-1 receptor agonist, meaning it mimics two gut hormones simultaneously. Wegovy contains semaglutide, made by Novo Nordisk, and targets the GLP-1 receptor only. In practical terms, activating the GIP pathway alongside GLP-1 appears to produce a stronger appetite-suppressing signal for many people. Whether that translates to greater weight loss in any individual is a clinical question, not a marketing one.

Both medicines are licensed in the UK for adults with a BMI of 30 or above, or 27 or above alongside at least one weight-related condition such as high blood pressure, high cholesterol or obstructive sleep apnoea. Both carry Black Triangle (▼) status with the MHRA, meaning they're subject to additional monitoring. And both are prescription-only medicines: a prescriber assesses your full picture before issuing one.

If you're trying to understand how the broader landscape of injectable weight-loss medicines sits, our Wegovy overview covers semaglutide's licensed uses in more depth.

What the trial evidence actually says about weight loss

The headline trial figures are the most concrete way to compare. SURMOUNT-1 tested tirzepatide over 72 weeks in thousands of adults with obesity; participants on the 15mg dose achieved around 20–21% average body-weight reduction. STEP 1 tested semaglutide 2.4mg over 68 weeks; participants averaged roughly 15% weight reduction. Both trials were conducted in adults without type 2 diabetes, alongside lifestyle changes, and both are published in the New England Journal of Medicine.

A direct head-to-head comparison came from the SURMOUNT-5 trial (72 weeks, 751 adults with obesity), which found tirzepatide produced greater average weight reduction than semaglutide 2.4mg. If you'd like a detailed breakdown, our guide to what's the difference between Monjaro and Wegovy walks through the clinical evidence side by side. NICE's appraisal of tirzepatide (TA1026) references this indirect and direct evidence in favouring tirzepatide's efficacy profile.

One number worth knowing: Novo Nordisk's Wegovy 7.2mg dose (approved by the MHRA on 14 April 2026 as a dedicated single-dose pen) reported around 20.7% average weight loss over 72 weeks, notably narrowing the gap with tirzepatide 15mg. So the comparison isn't static; both medicines are still evolving.

These are population averages from controlled trials. Individual results depend on starting weight, adherence, dose reached, lifestyle changes and biology. No medicine guarantees a specific outcome for any one person.

Note on Ozempic: semaglutide is also sold as Ozempic, but that product is licensed for type 2 diabetes, not weight management. If you've been reading about Ozempic for weight loss, our page on the difference between Ozempic and Wegovy clarifies the distinction.

Side effects, starting doses and what the titration schedule means for you

Both medicines share a broadly similar side-effect profile because both slow gastric emptying. Nausea, loose stools, constipation, indigestion, burping and fatigue are the most commonly reported, and they're most noticeable early in treatment or after a dose increase. For most people they settle over days to a couple of weeks. Injection-site reactions can occur with either, and both should be stored in the fridge.

Mounjaro starts at 2.5mg, a dose whose job is helping your system adjust, titrated upward by your prescriber typically in four-week steps. The prescriber decides the pace and the ceiling, not you. Wegovy follows a similar escalating path from 0.25mg to 2.4mg (now up to 7.2mg for eligible patients).

There's one practical difference worth flagging: for women on oral contraceptives, the NHS England guidance on weight-management injections advises adding a non-oral contraceptive method for the first four weeks of Mounjaro treatment and for four weeks after each dose increase, because tirzepatide may reduce pill absorption. There's no equivalent guidance for semaglutide. If you're on oral contraception, tell your prescriber before starting either medicine.

For a fuller look at how Saxenda compares with Wegovy, see our Saxenda vs Wegovy page.

How to decide, and what our prescribers consider

If you're ordering by 12pm on a weekday, a GPhC-registered Independent Prescriber at our pharmacy reads your consultation answers the same day. They look at your BMI, medical history, current medicines, any conditions that raise contraindications, and what dose journey is realistic for you, not just which headline number looks bigger.

Some people have a clinical reason to prefer one medicine over the other. Some have tried semaglutide and want to discuss switching. Some are starting from scratch and want the option with the stronger efficacy data, and our page covering the difference between Manjaro and Wegovy is a useful starting point for those conversations. All of those are valid conversations, and they're exactly the kind our prescribers have. You can read more about how we approach clinical oversight on our clinical team page.

Which medicine suits you is a clinical decision made with our prescribers, not a choice driven by which trial produced the bigger number. If you want a straightforward summary before you consult, our page on the difference between Manjaro and Wegovy sets out the key points clearly. If you're ready to have that conversation, start your free consultation and we'll take it from there.