Mounjaro vs Ozempic: What's the Real Difference?

"Mounjaro vs Ozempic" is one of the most searched comparisons in weight management, but in the UK the key answer is this: Mounjaro (tirzepatide) and Ozempic (semaglutide) are both used in type 2 diabetes management , while Ozempic is not licensed for weight loss, so the proper UK weight-loss comparison is usually Mounjaro vs Wegovy, the semaglutide brand approved for weight management. For adults in the UK looking at medically approved, prescription-only weight loss options, that distinction changes which treatments can actually be considered.

This guide explains why the licensing difference matters, how Mounjaro and semaglutide work, what clinical trials show about weight-loss results over time, how NICE guidance and NHS availability affect access, what side effects to weigh up, and how to discuss the most suitable option with your prescriber. In short, it's here to help you make sense of a common search term that can otherwise lead to the wrong comparison, and to make a clearer, evidence-based decision about legal, effective weight management treatment in the UK.

1. The Question Behind the Question: Ozempic, Wegovy, and What You're Really Comparing

Ozempic and Wegovy both contain the same active ingredient, semaglutide, manufactured by Novo Nordisk . What differs is the licensed use and the dose: Ozempic is available from 0.5 mg to 2 mg, while Mounjaro is available from 2.5 mg to 15 mg. In the UK:

• Ozempic (semaglutide, 0.5mg to up to 2mg) is licensed for type 2 diabetes only. The MHRA has been explicit that it is not authorised for weight loss, and using it off-label for that purpose has previously contributed to supply shortages for people who need it for diabetes.
• Wegovy (semaglutide) is the semaglutide brand licensed specifically for weight management in the UK .

This means that when most people search "Ozempic vs Mounjaro" wanting to compare weight-loss options, the medically accurate comparison is actually Wegovy vs Mounjaro, even though many people also compare Mounjaro with Ozempic when weighing up treatments. Both are licensed for weight management in the UK and may be supplied by regulated UK pharmacies following an appropriate clinical assessment ."Ozempic" is the term most people search, and because Ozempic is a genuinely relevant medicine, just for a different condition. Where this guide compares weight-loss outcomes, it's comparing tirzepatide with semaglutide at weight-management doses, which is what the clinical evidence below is actually based on.

Quick answer for a rushed reader

• Ozempic: licensed for type 2 diabetes in the UK, not weight loss.
• Wegovy: licensed for weight management, same active ingredient as Ozempic, higher dose.
• Mounjaro: licensed for both type 2 diabetes and weight management, under different NICE appraisals.
• For weight loss specifically, the fair comparison is Mounjaro vs Wegovy, not Mounjaro vs Ozempic.

2. What Are Mounjaro and Semaglutide (Ozempic/Wegovy)?

Mounjaro contains tirzepatide, a dual GIP and GLP-1 receptor agonist, the first of its kind approved in the UK. Ozempic and Wegovy both contain semaglutide, a GLP-1 receptor agonist. Both medicines are used, at different doses and under different licences, for type 2 diabetes and weight management. Both can improve blood glucose control, although treatment suitability and outcomes vary between individuals .

3. How Do the Mechanisms Actually Differ?

Semaglutide works on a single hormone pathway, GLP-1 (glucagon-like peptide-1), which is involved in regulating appetite, slowing gastric emptying, and supporting insulin release. Tirzepatide works on that same GLP-1 pathway and, in addition, on GIP (glucose-dependent insulinotropic polypeptide) receptors, and both pathways help regulate blood glucose as well as appetite. This dual mechanism is the core pharmacological difference between the two medicines, and it is one of the factors thought to contribute to differences observed in clinical studies .

4. What Does the Evidence Actually Show? The SURMOUNT-5 Trial

This is where direct comparative evidence is available and can be considered in context . SURMOUNT-5, a head-to-head randomised trial published in the New England Journal of Medicine, directly compared tirzepatide with semaglutide at their maximum tolerated weight-management doses (tirzepatide 10mg or 15mg vs semaglutide 1.7mg or 2.4mg) in 751 adults with obesity or overweight and at least one weight-related condition, over 72 weeks.

The trial reported an average body weight reduction of 20.2% with tirzepatide compared with 13.7% with semaglutide , a statistically significant difference. In the clinical trials data, 81.8% of people taking tirzepatide lost at least 5% of their starting weight. On a secondary measure, 31.6% of people taking tirzepatide achieved at least 25% body weight loss, compared with 16.1% of those taking semaglutide.

It's important to be precise about what this does and doesn't mean. This is trial-average data from a specific study population over a specific timeframe; individual results vary considerably, and this is how people lose weight in studies, not a guarantee for every person. Treatment suitability depends on an individual clinical assessment, and your prescriber will take a much wider range of factors into account than a single average figure from one trial.

Quick answer for a rushed reader

• SURMOUNT-5 (NEJM, 751 adults, 72 weeks): tirzepatide averaged 20.2% weight loss vs 13.7% with semaglutide.
• 31.6% of tirzepatide users reached ≥25% weight loss, vs 16.1% with semaglutide.
• This is average trial data, not a guarantee or a personal prediction. Individual response varies.

5. The Wider Evidence Base

Beyond the direct comparison, each medicine has its own substantial trial programme worth knowing about.

Tirzepatide's obesity evidence largely comes from the SURMOUNT trial programme, which supported its NICE approval for weight management. Semaglutide's evidence for weight management comes from the STEP trial programme, and semaglutide also has cardiovascular outcome evidence from the SELECT trial, which reported cardiovascular outcome benefits in the study population examined in adults with overweight or obesity and existing cardiovascular disease, supporting its use for cardiovascular risk reduction alongside weight management in eligible patients; In some countries, semaglutide has additional licensed indications relating to cardiovascular risk reduction .

6. NICE Guidance and NHS Availability

Both medicines have been appraised by NICE for weight management, though under separate appraisals with their own eligibility criteria.

• Mounjaro (tirzepatide) is covered by NICE TA1026, recommending it for adults with an initial body mass index (BMI) of at least 35 kg/m² and eligible comorbidities, which can include a weight-related health condition such as high blood pressure (with a lower threshold applied for certain ethnic groups, in line with NICE's standard adjusted BMI thresholds), alongside a reduced-calorie diet and increased physical activity. NHS rollout is being phased in over several years due to capacity constraints, with prioritised patient cohorts accessing it first.
• Wegovy (semaglutide) is covered by NICE TA875, recommending it for eligible adults through specialist weight management services, also alongside diet and exercise support.

NHS access to either medicine for weight management is limited by capacity and eligibility criteria, which is why many people access these treatments privately through a regulated UK pharmacy following a clinical assessment. Private treatment costs and access routes can vary .

7. Is Mounjaro Better Than Ozempic (or Wegovy)?

A balanced interpretation of the evidence is important : the main difference in trial evidence is that tirzepatide produced a greater average weight reduction than semaglutide, although individual suitability still matters. That was a statistically significant finding within the trial population studied . But "better on average across a trial population" isn't the same as "better for you specifically," because the way each medication affects tolerability and response can differ from person to person. Individual factors, including how your body responds, your medical history, other medicines you take, and side effect tolerability, are among the factors that help determine which treatment may be most appropriate . Your prescriber will determine the appropriate treatment based on your individual circumstances, not a single trial average.

8. Side Effects: How Do They Compare?

Both tirzepatide and semaglutide commonly cause gastrointestinal side effects, particularly nausea and stomach discomfort, when starting treatment or moving from a lower dose to a higher dose, which is consistent with how both drug classes work by slowing gastric emptying. The SURMOUNT-5 trial reported that tirzepatide's safety profile was broadly consistent with earlier SURMOUNT trials, with gastrointestinal effects being the most commonly reported adverse events for both medicines and no significant difference in serious adverse events in some analyses. Gastrointestinal side effects are among the most commonly reported adverse effects with both medicines . In some studies, side effects have led some participants to discontinue treatment . Individual tolerability varies, and some people find they tolerate one medicine notably better than the other. If side effects are severe, persistent, or concerning, contact your prescriber, especially as both medicines may require supervision for risks such as low blood sugar in some patients, and both include important safety warnings and precautions, including those relating to pancreatitis ; allergic reactions, including a serious allergic reaction, are rare but need urgent medical attention if symptoms occur.

9. Who Might Be Considered for Which Treatment?

This is general context to help you think it through, not a recommendation for your specific situation. Treatment suitability depends on an individual clinical assessment. Prescribers may also consider whether the goal is diabetes management, chronic weight management, or another weight loss treatment pathway.

• Some people may wish to discuss alternative treatment options with their prescriber if they have not achieved their desired outcomes with a previous treatment .
• Treatment choice may also be influenced by factors such as clinical history, treatment goals, and prescriber recommendation , and Ozempic may sometimes be considered when blood sugar or cardiovascular factors are central.
• Anyone with a history of certain thyroid cancers, pancreatic conditions, or who is pregnant, trying to conceive, or breastfeeding should discuss this directly with a prescriber before either medicine is considered, since these are relevant to both; prescribing decisions also depend on medical history, contraindications, and whether the aim is to treat weight loss under a licensed route.

Key Takeaways

• Ozempic is licensed in the UK for type 2 diabetes only. Wegovy, not Ozempic, is the licensed semaglutide option for weight management, although Ozempic remains one of the diabetes drugs people often ask about in this comparison.
• Mounjaro (tirzepatide) works on two hormone pathways; semaglutide works on one.
• The SURMOUNT-5 head-to-head trial found greater average weight loss with tirzepatide than with semaglutide over 72 weeks , though individual results vary.
• Both Mounjaro and Wegovy have NICE approval for weight management (TA1026 and TA875 respectively).
• Treatment suitability depends on an individual clinical assessment. A trial average doesn't predict your individual outcome, and long term weight management still depends on ongoing clinical follow-up plus diet and exercise to support a healthy weight.