The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Mounjaro vs Wegovy: UK Prices, Doses & How They Compare
Comparing Mounjaro and Wegovy in the UK? Both are prescription-only weight loss injections, but they work differently and have different costs. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trial data shows different average weight loss results, and UK pricing varies by dose and provider. This guide compares both medications factually to help you understand the differences—though which is right for you depends on your individual health and requires a prescriber assessment.
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What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Clinical Mechanism & Trial Data: Mounjaro vs Wegovy
Mounjaro (tirzepatide) activates two hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1. This dual action may support appetite regulation and fat utilisation differently than single-pathway medications. In the SURMOUNT-1 clinical trial, participants on the maximum 15mg dose lost an average of 20.9% of body weight over 72 weeks.
Wegovy (semaglutide) activates the GLP-1 pathway only. In the STEP-1 clinical trial, participants on 2.4mg lost an average of 14.9% of body weight over 68 weeks. Both medications were used alongside a reduced-calorie diet and increased physical activity.
- Mounjaro: doses from 2.5mg to 15mg weekly
- Wegovy: doses from 0.25mg to 2.4mg weekly
- Individual results vary significantly
- Trial data represents averages, not assured outcomes
Your GP or prescriber will assess which mechanism may suit your health profile best.
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Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
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UK Pricing, Access & Prescriber Assessment
UK pricing for both medications varies by dose and provider. Private online prescribing typically costs £129–£320 per month depending on dose. NHS access is limited to specialist tier 3 weight management services—availability and waiting times vary significantly by region.
Both Mounjaro and Wegovy require a clinical assessment by a UK-licensed prescriber before prescription. Eligibility criteria are similar: BMI of 30 or above, or 27–29.9 with weight-related health conditions (diabetes, hypertension, sleep apnoea). Use our GLP-1 weight loss calculator to estimate potential outcomes at different doses, and our BMI calculator to check your starting point. Your prescriber will discuss which medication aligns with your health needs, medical history, and lifestyle.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Is Mounjaro more effective than Wegovy for weight loss?
Clinical trials showed Mounjaro had slightly higher average weight loss (20.9% vs 14.9%), but these are averages—individual results vary significantly. Effectiveness depends on your personal response, adherence, diet, and activity level. Your prescriber will assess which is more suitable based on your health profile, not just average trial data.
Why is Mounjaro more expensive than Wegovy in the UK?
Pricing varies by provider and dose. Mounjaro's maximum dose (15mg) targets more severe cases and may have higher manufacturing costs. Wegovy has a lower maximum dose (2.4mg). Both are subject to UK pricing models set by manufacturers and distributors. Always compare current prices with registered online prescribers.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications should only be done under prescriber guidance. There's no official established conversion chart between the two. Your prescriber will manage any switch carefully, considering your current response and adjusting doses appropriately. Never switch without clinical advice.
Which is available on the NHS in the UK?
Both Mounjaro and Wegovy are approved for NHS prescribing through specialist tier 3 weight management services. However, NHS availability is limited and varies significantly by region. Access typically requires GP referral and specialist assessment. Private prescribing offers faster access but at a cost.
Do Mounjaro and Wegovy have different side effects?
Both share similar common side effects: nausea, diarrhoea, vomiting, constipation, and stomach pain. Side effect profiles are comparable because both are GLP-1 pathway activators. Individual tolerability varies. Your prescriber will discuss side effect management and monitoring for your chosen medication.
Ready to take control of your weight loss journey?
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