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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Mounjaro on NHS Criteria vs Wegovy
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but understanding the NHS eligibility criteria and how they compare can help you have an informed conversation with your GP. This guide explains the clinical differences, trial evidence, and what it means for your personal suitability assessment. Use our free BMI calculator above to check where you stand against NHS thresholds.
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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 Mechanism Differences
The key difference between Mounjaro and Wegovy lies in how they work. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways simultaneously, whereas Wegovy (semaglutide) is a GLP-1 receptor agonist only, targeting a single pathway. In the SURMOUNT-1 clinical trial, Mounjaro at maximum dose (15 mg) achieved average weight loss of approximately 20.9% of body weight over 72 weeks. In the STEP-1 trial, Wegovy at maximum dose (2.4 mg) achieved average weight loss of approximately 14.9% over 68 weeks. Both trials involved participants following a reduced-calorie diet and increasing physical activity — results are average figures and individual outcomes vary significantly. The dual mechanism of Mounjaro may explain the slightly higher average weight loss, though both medications help regulate appetite and food intake through GLP-1 pathways.
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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.
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NHS Eligibility and Individual Suitability
Both Mounjaro and Wegovy have identical NHS eligibility criteria: adults with a BMI of 30 kg/m² or above, or 25–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, prediabetes, high blood pressure, or sleep apnoea. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply (from BMI 27.5). Which medication is prescribed depends on individual clinical assessment, not criteria alone. Your GP or prescriber will review your medical history, current medications (particularly oral contraceptives and diabetes treatments), and personal preferences. Both require a prescription and clinical assessment — neither is available without healthcare professional evaluation. Neither medication is NHS-funded as standard; access through NHS specialist tier 3 weight management services depends on regional availability and funding.
- 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 contains tirzepatide and acts as a dual GIP and GLP-1 receptor agonist, activating two hormone pathways. Wegovy contains semaglutide and is a GLP-1 receptor agonist only. This dual mechanism may contribute to Mounjaro's slightly higher average weight loss in clinical trials, though both medications work on appetite regulation and help people feel fuller with smaller meals.
Do Mounjaro and Wegovy have the same NHS eligibility criteria in the UK?
Yes, both medications have identical NHS eligibility criteria: BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, NHS recommends lower thresholds starting from BMI 27.5. Individual prescribing decisions depend on clinical assessment by your GP or specialist.
How much weight loss can I expect with Mounjaro vs Wegovy?
In clinical trials, Mounjaro achieved average weight loss of approximately 20.9% of body weight, while Wegovy achieved approximately 14.9%. However, these are trial averages — individual results vary significantly based on diet, exercise, adherence, and personal metabolism. Always use conditional language: results "may help" but are not assured.
Can I switch between Mounjaro and Wegovy on the NHS?
Switching between medications is possible but requires prescriber assessment and guidance. Approximate dose equivalences exist (Mounjaro 5 mg ≈ Wegovy 0.5 mg), but there is no official conversion chart. Any medication switch must be managed by your GP or specialist — never attempt to switch doses independently.
How do I access Mounjaro or Wegovy through the NHS?
Access is through NHS specialist tier 3 weight management services, typically via GP referral. Availability and waiting times vary significantly by region (integrated care board). Many areas have substantial waiting lists. Private prescription access is available through GPhC-registered online pharmacies following clinical assessment, though this involves private costs ranging from approximately £129–£320 per month depending on dose.
Ready to take control of your weight loss journey?
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