Ozempic vs Wegovy vs Mounjaro: what's the difference?

Medically reviewed by Muhammad A Jalil, Superintendent Pharmacist (GPhC Reg No: 2236161)

Published 2026-08-22 · Clinically reviewed 2026-08-22 · Updated 2026-08-23

Wegovy and Ozempic both contain semaglutide; Mounjaro contains tirzepatide. How the three medicines differ in UK licensing, dosing and results.

Ozempic, Wegovy and Mounjaro are the three names most people have heard in connection with medical weight loss, but they are not interchangeable. Wegovy and Ozempic contain the same active ingredient, semaglutide, yet only Wegovy is licensed in the UK for weight management — Ozempic is licensed for type 2 diabetes. Mounjaro contains a different medicine altogether, tirzepatide, and is licensed for both type 2 diabetes and weight management. In practice, a UK clinician treating weight will normally be choosing between Wegovy and Mounjaro.

What does each medicine contain?

Semaglutide, the active ingredient in both Wegovy and Ozempic, is a GLP-1 receptor agonist. It mimics glucagon-like peptide-1, a hormone your gut releases after eating, which reduces appetite, helps you feel full sooner and slows stomach emptying. Tirzepatide, the active ingredient in Mounjaro, goes a step further: it acts on the GLP-1 receptor and on a second gut-hormone receptor called GIP, which is thought to add to its effect on appetite and metabolism.

All three are taken as a once-weekly injection from a pre-filled pen, starting at a low dose that is stepped up gradually over several months to improve tolerability. Our guide to how GLP-1 weight-loss treatments work explains the biology in more detail.

Which are licensed for weight management in the UK?

Medicine	Active ingredient	UK licence	Typical dosing
Wegovy	Semaglutide	Weight management	Weekly injection, stepped up to 2.4 mg
Ozempic	Semaglutide	Type 2 diabetes only	Weekly injection, up to 2 mg
Mounjaro	Tirzepatide	Type 2 diabetes and weight management	Weekly injection, stepped up to 15 mg

Because Ozempic's licence covers type 2 diabetes only, prescribing it for weight loss is off-label. UK regulators and pharmacy bodies have asked prescribers not to do this, partly because past shortages left people with diabetes struggling to get their medicine. A regulated UK weight-loss service will therefore assess you for Wegovy or Mounjaro rather than Ozempic.

How do the results compare?

In the STEP 1 trial, adults taking semaglutide 2.4 mg alongside diet and activity support lost around 15% of their body weight on average over 68 weeks, compared with about 2.4% with placebo. In SURMOUNT-1, adults taking the highest dose of tirzepatide lost around 20% on average over 72 weeks. A later head-to-head study comparing the two medicines directly found a greater average loss with tirzepatide.

Averages hide enormous individual variation. Some people respond strongly to semaglutide and modestly to tirzepatide, and a minority lose little weight with either. Every major trial also paired the medicine with dietary and activity changes — the injections support those changes rather than replace them.

What about side effects?

The two medicines share a very similar side-effect profile. Nausea, constipation, diarrhoea and reflux are the most common problems, particularly in the weeks after a dose increase, and usually settle as your body adjusts. Less common but important risks include gallstones and pancreatitis — severe, persistent stomach pain needs urgent medical attention.

Neither medicine should be used during pregnancy or breastfeeding, and both should be stopped in advance if you are planning a pregnancy. If you take diabetes medicines such as insulin or sulfonylureas, doses may need adjusting to avoid low blood sugar. Your prescriber will go through your full medical history before recommending either treatment.

Which one is right for you?

This is not a decision to make on brand recognition. A prescriber will weigh your BMI and any weight-related conditions, your medical history, medicines you already take, how you responded to any previous treatment, availability, and your own preferences. Broadly, UK licensing supports treatment from a BMI of 30, or from 27 alongside a weight-related condition such as high blood pressure — but the assessment is always individual.

One caution: counterfeit pens have been found in the UK when people obtain these medicines from unregulated sellers. A legitimate UK service is registered with the General Pharmaceutical Council and will always ask you to complete a medical consultation before any medicine is prescribed.

Frequently asked questions

Can I switch between Wegovy and Mounjaro?

Yes, with clinical oversight. The two medicines are not dose-for-dose equivalent, so your prescriber will usually restart you at a lower step of the new medicine and build up again, timing the switch around your last dose.

Why can't I get Ozempic for weight loss in the UK?

Its licence covers type 2 diabetes only, and regulators have asked prescribers to protect supply for people with diabetes. The same active ingredient is available for weight management as Wegovy.

Will I regain weight if I stop?

Trial follow-ups show that gradual regain is common after stopping treatment, which is why reputable services focus on the eating, activity and sleep habits you build while on the medicine — and on a planned, supported approach to coming off it.

Are these medicines available on the NHS?

Access is limited. Wegovy is available through specialist NHS weight-management services, and tirzepatide is being introduced in phases for people with the greatest clinical need. Many people currently access treatment privately, but the same eligibility rules apply.

If you are considering treatment, the right starting point is a structured medical assessment rather than a brand name. You can check your eligibility for our weight-loss programme online — a UK prescriber reviews every consultation, and treatment is only recommended when it is clinically appropriate.