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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Who Qualifies For Mounjaro? Mounjaro vs Wegovy
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but eligibility and how they work differ. To qualify for either medication, you'll need a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. This guide compares both medications to help you understand which might suit your situation — though your prescriber will make the final clinical assessment.
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Calculate Your BMI Instantly
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 Work — Clinical Mechanism
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in the body. This dual mechanism may help regulate appetite and blood sugar control simultaneously. In the SURMOUNT-1 clinical trial, participants taking Mounjaro at the maximum 15 mg dose lost an average of 20.9% of their body weight over 72 weeks.
Wegovy (semaglutide) is a single GLP-1 receptor agonist — it activates only the GLP-1 pathway. In the STEP-1 clinical trial, participants on the maximum 2.4 mg dose lost an average of 14.9% of body weight over 68 weeks. Both medications slow gastric emptying and signal fullness to the brain, supporting smaller meal portions and reduced food cravings.
Neither medication is insulin, and both are used alongside reduced-calorie diet and increased physical activity for best results. Individual results vary significantly, and what works best for one person may differ for another.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
UK Eligibility and Prescriber Assessment
You may qualify for either medication in the UK if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions. These conditions include type 2 diabetes, prediabetes, hypertension, abnormal blood lipids, obstructive sleep apnoea, or a history of cardiovascular disease. For South Asian, Chinese, Black African, and Black Caribbean adults, lower BMI thresholds often apply (eligibility may start at BMI 27.5). A UK-licensed prescriber will assess your individual health profile, medical history, and suitability during a clinical consultation. Both Mounjaro and Wegovy require a prescription — access is available through NHS specialist weight management services or private online prescribing. Use our free BMI calculator above to check where your weight sits, and our GLP-1 weight loss calculator to see projected outcomes at different doses.
- 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 uses dual GIP and GLP-1 mechanisms, while Wegovy uses GLP-1 only. Clinical trials showed Mounjaro achieved higher average weight loss (~20.9% vs ~14.9% on Wegovy), though individual results vary. Both are once-weekly injections and require prescription and clinical assessment.
Can I switch from Wegovy to Mounjaro, or vice versa?
Switching between medications must be managed by your prescriber. There is no official UK conversion chart between the two — approximate dose equivalences exist (e.g. Wegovy 2.4 mg ≈ Mounjaro 15 mg), but any switch requires medical supervision and reassessment.
Do I qualify for either medication on the NHS?
NHS access is through specialist tier 3/4 weight management services. You'll need GP referral and must meet BMI criteria with relevant health conditions. Availability and waiting times vary significantly by region. Private online prescribing is also available without NHS referral if you meet eligibility criteria.
Which medication loses more weight — Mounjaro or Wegovy?
Clinical trial data suggests Mounjaro achieves slightly higher average weight loss, but individual results vary widely. Your prescriber will recommend the most suitable option based on your health profile, not just trial averages. Both require lifestyle changes (diet and exercise) alongside medication.
How do I start the process to get either medication prescribed?
Contact your GP for NHS referral to a specialist weight management service, or use a private online prescriber registered in the UK. A clinical assessment will check your BMI, health conditions, medication interactions, and suitability. Our free BMI calculator can help you understand your current status before you book a consultation.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.