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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Wegovy Criteria vs Mounjaro — Who Qualifies?
Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are prescription-only GLP-1 receptor agonist medications licensed in the UK for weight management. However, they differ in their mechanisms, trial outcomes, and how prescribers assess suitability. Understanding the eligibility criteria for each and how they compare helps you have informed conversations with your GP or prescriber. Use our free GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to check your starting point.
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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.
Clinical Trial Data and Mechanism Differences
Wegovy (semaglutide) is a single GLP-1 receptor agonist that activates one hormone pathway. The STEP-1 clinical trial showed participants lost an average of approximately 14.9% of body weight over 68 weeks on the maximum dose of 2.4 mg.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two pathways. The SURMOUNT-1 trial showed participants lost an average of approximately 20.9% of body weight on the maximum dose of 15 mg over 72 weeks.
This dual mechanism may explain why some people achieve greater weight loss with Mounjaro, though individual results vary significantly and response depends on many factors including diet, activity level, genetics, and adherence. Both medications are used alongside a reduced-calorie diet and increased physical activity — neither works in isolation. Your prescriber will assess which mechanism suits your individual health profile.
Clinically BackedWeight Loss
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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 Individual Suitability Assessment
Both Wegovy and Mounjaro share the same basic UK eligibility criteria: BMI of 30 kg/m² or above, or BMI of 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, prediabetes, hypertension, dyslipidaemia, obstructive sleep apnoea, or cardiovascular history). For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds may apply (starting at BMI 27.5).
The choice between Wegovy and Mounjaro depends on individual factors: existing medications, side effect tolerance, injection frequency preference (both once-weekly), kidney function, and prescriber experience. Neither is inherently "better" — suitability is personal. Your prescriber will assess your full medical history, conduct blood tests if needed, and recommend the medication most likely to be safe and effective for you.
- 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 Wegovy and Mounjaro?
Wegovy is a single GLP-1 receptor agonist. Mounjaro is a dual GIP and GLP-1 agonist, activating two hormone pathways. This dual mechanism may result in greater average weight loss with Mounjaro, though individual responses vary. Both require prescription and clinical assessment in the UK.
Are the UK eligibility criteria the same for both?
Yes. Both require BMI ≥30 or BMI 27–29.9 with weight-related health conditions. For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds apply (BMI ≥27.5). Specific suitability is assessed individually by your prescriber based on medical history, medications, and blood tests.
Which medication will I lose more weight on?
Clinical trials show Mounjaro participants lost approximately 20.9% on average, while Wegovy participants lost approximately 14.9%. However, individual results vary widely based on genetics, diet adherence, physical activity, and personal metabolism. Your prescriber cannot assures specific outcomes for you personally.
Can I switch from Wegovy to Mounjaro if I'm not losing enough weight?
Potentially, yes — but only under prescriber guidance. There is no official conversion chart between the two. Any medication change requires clinical assessment and typically involves a waiting period. Discuss options with your prescriber rather than switching independently.
How do I know which medication is right for me?
Your prescriber will assess your full medical history, current medications, kidney function, and health conditions. Both are prescription-only and require clinical assessment. Neither is suitable for everyone. Your GP or prescriber will recommend the one most likely to be safe and effective for your individual circumstances.
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.