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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NHS Mounjaro Criteria vs Wegovy — Who Qualifies?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available through NHS specialist services in the UK, but eligibility criteria, mechanisms, and trial outcomes differ. Understanding the distinction helps you have informed conversations with your GP about which option might be suitable for your individual health needs. Both require clinical assessment and work best alongside lifestyle changes.
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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 Trial Data and How They Work Differently
Mounjaro and Wegovy show different weight loss profiles in clinical trials. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways simultaneously. The SURMOUNT-1 trial showed average weight loss of approximately 20.9% of body weight at the maximum 15 mg dose over 72 weeks. Wegovy (semaglutide) is a GLP-1-only receptor agonist. The STEP-1 trial demonstrated average weight loss of approximately 14.9% at the maximum 2.4 mg dose over 68 weeks. Both trials included participants following a reduced-calorie diet and increased physical activity. The key difference lies in mechanism: Mounjaro's dual action may produce greater appetite suppression for some individuals, whilst Wegovy's single pathway approach has a longer clinical track record in weight management. Individual responses vary significantly — some people respond better to one mechanism than the other.
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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.
NHS Eligibility and Prescriber Assessment
Both Mounjaro and Wegovy have identical NHS eligibility thresholds in the UK. You may qualify if you have a BMI of 30 kg/m² or above, or BMI of 27–29.9 kg/m² with a weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply. Access is through specialist tier 3 or 4 NHS weight management services, not standard GP prescription. A prescriber will assess your individual health, medications, and suitability — neither medication is automatically prescribed based on BMI alone. Use our free BMI calculator to check where you fall, then discuss your options with your GP for possible referral to specialist services.
- 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 is the main difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist activating two hormone pathways, whilst Wegovy (semaglutide) is a GLP-1-only agonist. This difference in mechanism may result in different weight loss outcomes for different individuals. Clinical trials showed Mounjaro achieved higher average weight loss (20.9%) compared to Wegovy (14.9%), but individual results vary significantly.
Are NHS eligibility criteria the same for both medications?
Yes. Both Mounjaro and Wegovy require a BMI of 30 or above, or 27–29.9 with weight-related health conditions. For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds apply. Access is only through NHS specialist weight management services, not standard GP prescription.
Which medication is more likely to be prescribed on the NHS?
NICE has approved both tirzepatide (Mounjaro) and semaglutide (Wegovy) for NHS use, but regional availability, funding, and specialist service capacity vary significantly across England. Some regions may have one available before the other, or neither may currently be funded. Your specialist prescriber will discuss which option is suitable for you.
Can I switch from Wegovy to Mounjaro on the NHS?
Switching between medications requires prescriber guidance. Approximate dose equivalence exists (e.g., Wegovy 2.4 mg ≈ Mounjaro 15 mg), but any switch must be managed by your healthcare team. There is no official NHS conversion protocol — your prescriber will assess suitability and manage any transition carefully.
How long does it take to access Mounjaro or Wegovy through the NHS?
Wait times vary considerably by region and specialist service capacity. Referral to tier 3 weight management services can take months, and medication initiation may follow further assessment. Private prescription options are available more quickly but involve cost. Discuss timelines with your GP when requesting referral.
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.