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 on the NHS — How They Compare
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections licensed in the UK, but they work differently and have different access routes through the NHS. Understanding the differences can help you and your GP make an informed decision about which, if either, might be suitable for you. This guide compares the two medications factually based on clinical trial data and NHS guidance.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
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.
How Mounjaro and Wegovy Differ — Mechanism and Trial Results
Mechanism of action: The key difference is that Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 receptor agonist only. This means Mounjaro activates two natural hormone pathways in the gut, whereas Wegovy activates one. Both support appetite regulation and feeling fuller after smaller meals, but the dual mechanism may contribute to Mounjaro's slightly higher weight loss outcomes in clinical trials.
- Mounjaro (tirzepatide): SURMOUNT-1 trial showed average weight loss of approximately 15–21% of body weight at the maximum 15mg dose over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide): STEP-1 trial showed average weight loss of approximately 14.9% of body weight at the maximum 2.4mg dose over 68 weeks, with the same lifestyle support.
Individual results vary significantly — these are clinical trial averages, not assured outcomes. Neither medication is suitable for everyone, and a prescriber will assess your individual health and eligibility.
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How It Works
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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NHS Access and Eligibility — Which Is Available to You?
Both Mounjaro and Wegovy are available through NHS specialist weight management services (tier 3), but access is limited and varies significantly by region. Your GP can refer you to your local specialist tier 3 weight management service, where clinicians will assess your eligibility based on your BMI, health conditions, and individual circumstances. Waiting lists can be very long in many areas — sometimes months to years.
If NHS waiting times are not suitable for your circumstances, both medications are available through private online prescribing services in the UK. A licensed prescriber will assess you via an online consultation and issue a prescription if clinically appropriate. Use our GLP-1 weight loss calculator above to explore potential outcomes at different doses, and our BMI calculator to check your current BMI category and see where you fall against NHS eligibility thresholds.
- 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 better than Wegovy?
Clinical trials show Mounjaro achieved slightly higher average weight loss (15–21% vs 14.9%), likely due to its dual GIP+GLP-1 mechanism. However, "better" depends on individual suitability, tolerability, and response. Both are effective for many people; a prescriber will assess which is more appropriate for you.
Can I get Mounjaro or Wegovy on the NHS?
Yes, both are available through NHS specialist tier 3 weight management services. You need a GP referral and assessment for eligibility based on BMI and health conditions. NHS availability and waiting times vary significantly by region. Private prescribing is also available in the UK without an NHS referral.
What's the difference between Mounjaro and Wegovy injections?
Mounjaro (tirzepatide) is a dual GIP+GLP-1 receptor agonist given once weekly at doses up to 15mg. Wegovy (semaglutide) is a GLP-1-only agonist given once weekly at doses up to 2.4mg. The dual mechanism of Mounjaro may explain slightly higher average weight loss, but individual response varies.
What's the starting dose for Mounjaro vs Wegovy on NHS?
Mounjaro starts at 2.5mg weekly and escalates gradually. Wegovy starts at 0.25mg weekly and escalates over several weeks. Doses are adjusted based on tolerability and response. A prescriber will tailor the dosing schedule to your individual needs.
How long do I take Mounjaro or Wegovy?
Both are typically continued long-term to maintain weight loss. If you stop either medication, weight may return. Duration depends on your goals and how well the medication works for you. Your prescriber will monitor progress and discuss ongoing suitability at regular reviews.
Ready to take control of your weight loss journey?
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