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 — Qualifications and Eligibility in the UK
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but eligibility criteria are identical for both medications. This guide compares their qualifications, explains the clinical assessment process, and helps you understand which might be suitable for your individual circumstances. Your GP or a licensed prescriber will assess your health profile to determine which option is appropriate.
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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.
Eligibility Requirements — Are You Qualified for Either Medication?
Both Mounjaro and Wegovy require the same UK eligibility criteria. You may be qualified if you have:
- BMI of 30 or above (obesity), or
- BMI of 27–29.9 (overweight) with at least one weight-related health condition
Weight-related conditions include type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, obstructive sleep apnoea, or history of cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply — eligibility may start at BMI 27.5 or above, reflecting higher cardiovascular and metabolic risk at lower weights. Our free BMI calculator above helps you check your current BMI instantly and understand where you fall on the NHS scale.
You cannot take either medication if you're under 18, pregnant, breastfeeding, or allergic to the active ingredient.
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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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Mechanism Differences — Why Qualifications Are the Same But Effects May Differ
Although both medications have identical qualification criteria, they work through different mechanisms. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways simultaneously. Wegovy (semaglutide) is a GLP-1 receptor agonist only, working through a single pathway. Clinical trials (SURMOUNT for Mounjaro, STEP for Wegovy) showed Mounjaro achieved average weight loss of 15–21% of body weight, whilst Wegovy achieved approximately 15%. However, individual results vary significantly, and the "best" medication depends on your medical history, other medications, and how your body responds. Your prescriber will discuss which is most suitable during your clinical assessment.
- 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.
Can I access both Mounjaro and Wegovy through the NHS in the UK?
Both are available through NHS tier 3 specialist weight management services following GP referral, though availability and waiting times vary significantly by region. Private access via GPhC-registered online pharmacies is also possible if you meet the clinical criteria and receive a prescription from a UK-licensed prescriber.
Do I need a lower BMI threshold if I'm of South Asian or Black African heritage?
Yes. The NHS recognises that South Asian, Chinese, Black African, and Black Caribbean adults face higher cardiometabolic risk at lower BMI levels. For these groups, eligibility for weight loss medication typically starts at BMI 27.5 or above, rather than 30, reflecting updated risk assessment guidance.
What's the difference between the clinical trials for Mounjaro and Wegovy?
Mounjaro was evaluated in the SURMOUNT-1 trial, showing average weight loss of 15–21% depending on dose. Wegovy was evaluated in the STEP-1 trial, showing average weight loss of approximately 15%. Both trials included reduced-calorie diet and increased physical activity. Results are not directly comparable because trial populations differed, but both demonstrate clinically meaningful weight loss.
Which medication should I choose — Mounjaro or Wegovy?
Both have identical qualification criteria, so eligibility is not the differentiator. The choice depends on individual factors including your medical history, other medications you take, potential side effect tolerance, and prescriber clinical judgment. Your GP or licensed prescriber will assess these factors and recommend the most suitable option for you.
Do I need different qualifications if I'm accessing weight loss medication privately versus through the NHS?
No. Clinical eligibility is the same regardless of access route. Whether you're referred to NHS specialist services or assessed by a private online prescriber, you must meet the same BMI and health condition criteria. A prescriber must still conduct a proper clinical assessment before issuing a prescription.
Ready to take control of your weight loss journey?
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