The UK's most complete GLP-1 guide
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- 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 Eligibility Criteria Compared
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections licensed in the UK, but eligibility criteria and clinical features differ. This guide explains the key differences to help you understand which medication a prescriber might recommend based on your individual health profile. Both require a clinical assessment before prescription, and your GP or licensed prescriber will determine suitability for you.
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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.
Clinical Mechanism and Trial Evidence — Key Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways in the body. In the SURMOUNT-1 clinical trial, participants achieved an average weight loss of approximately 20.9% of their body weight at the maximum 15mg dose over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates a single hormone pathway. In the STEP-1 clinical trial, participants achieved an average weight loss of approximately 14.9% of their body weight at the maximum 2.4mg dose over 68 weeks, also with dietary and lifestyle support.
Important note: these are clinical trial averages. Individual results vary significantly, and both medications require ongoing lifestyle changes to be effective. A prescriber will assess which mechanism may suit your specific health needs.
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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 Eligibility Criteria — Who Qualifies for Each?
Both Mounjaro and Wegovy have identical NHS and private eligibility criteria in the UK. You may qualify if you have a BMI of 30 or above, or a BMI of 27–29.9 with a weight-related health condition (such as type 2 diabetes, high blood pressure, or sleep apnoea). For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds typically apply.
The choice between Mounjaro and Wegovy is not based on eligibility — both require the same assessment criteria. Instead, your prescriber will consider factors such as medical history, other medications, side effect profile, and whether the dual-action mechanism of Mounjaro or single-action of Wegovy may suit you better. Use our free BMI calculator above to check your current BMI and assess your starting point.
Prescription access in the UK is available through two routes: NHS specialist tier 3 weight management services (following GP referral, with significant regional waiting lists), or private online prescribing services (following an online clinical assessment with a UK-licensed prescriber, with faster access but at cost). Your GP can discuss NHS options with you, or you can pursue private assessment independently. Either route requires a full clinical assessment — a prescriber will review your health history, current medications (especially if you take oral contraceptives or diabetes medications), and suitability before prescribing.
- 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.
What's the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist (activating two hormone pathways), while Wegovy is a GLP-1 receptor agonist only (one pathway). Clinical trials show Mounjaro resulted in slightly higher average weight loss (~20.9% vs ~14.9%), though individual results vary. Both require prescription and clinical assessment.
Do I need to meet different criteria for Mounjaro versus Wegovy?
No. Both medications have identical eligibility criteria in the UK: BMI 30 or above, or BMI 27–29.9 with weight-related conditions. Lower thresholds apply for certain ethnic backgrounds. The choice between them is based on individual health factors, not eligibility criteria.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching is possible but must be managed by your prescriber. There is no official established conversion between the two — approximate equivalences exist (e.g. Wegovy 0.5mg ≈ Mounjaro 5mg), but your prescriber will determine the safest switching protocol based on your current dose and health status.
How do I access Mounjaro or Wegovy in the UK?
Access is available through NHS specialist weight management services (referral from your GP; varies by region) or private online prescribing (following clinical assessment with a UK-licensed prescriber). Both routes require a full health assessment. Use our GLP-1 weight loss calculator to estimate potential outcomes.
Which medication should I choose — Mounjaro or Wegovy?
This is a clinical decision made by your prescriber based on your individual health history, medications, side effect tolerance, and medical profile — not your personal preference. Your GP or private prescriber will assess you and recommend the most suitable option. Both are effective alongside a reduced-calorie diet and increased physical activity.
Ready to take control of your weight loss journey?
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