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 and Wegovy NHS Requirements — What's the Difference?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but their eligibility criteria and clinical mechanisms differ slightly. Understanding the NHS requirements for each — and how they compare — helps you know what to expect when discussing weight management with your GP or specialist prescriber. Both require a clinical assessment before prescription.
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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 Each Medication Works
The key difference between Mounjaro and Wegovy lies in their mechanism. Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously, whereas Wegovy is a GLP-1 agonist only, activating a single pathway. This dual mechanism may explain why clinical trials showed different weight loss averages. In the SURMOUNT-1 trial, Mounjaro at its maximum dose (15 mg) helped participants lose approximately 20.9% of their body weight on average over 72 weeks. The STEP-1 trial showed Wegovy (2.4 mg) achieved approximately 14.9% average weight loss over 68 weeks. However, individual results vary significantly, and both medications work best alongside a reduced-calorie diet and increased physical activity. Use our free GLP-1 weight loss calculator to explore projected results at different doses, though actual outcomes depend on your personal response and lifestyle changes.
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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: Same Thresholds, Individual Assessment
Both Mounjaro and Wegovy share identical NHS eligibility criteria in the UK. You may be considered for either medication if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² with at least one weight-related health condition (such as type 2 diabetes, high blood pressure, abnormal cholesterol, sleep apnoea, or cardiovascular disease). For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds apply (BMI 27.5 or above). However, NHS access via specialist tier 3 weight management services varies by region and availability. Private prescription is also available through UK-licensed prescribers following an online clinical assessment. Your prescriber will assess which medication — if either — is most suitable based on your individual health profile, medical history, and any medications you're currently taking.
- 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.
Is Mounjaro more effective than Wegovy for weight loss on the NHS?
Clinical trials show Mounjaro achieved higher average weight loss (approximately 20.9% vs 14.9%), but this doesn't mean it's "better" — individual results vary widely, and the best medication is the one your prescriber deems safe and suitable for you. Both are evidence-based options.
Do I have the same NHS eligibility requirements for both Mounjaro and Wegovy?
Yes. Both require a BMI of 30 or above, or 27–29.9 with a weight-related health condition. Lower thresholds apply for people of South Asian, Chinese, Black African, or Black Caribbean heritage. Your prescriber will assess individual suitability.
What's the difference between a GLP-1 agonist and a dual GIP+GLP-1 agonist?
Wegovy activates one hormone pathway (GLP-1), whilst Mounjaro activates two pathways (GIP and GLP-1) simultaneously. The dual mechanism may enhance appetite regulation, though both support weight loss through similar effects on satiety and gastric emptying.
Can the NHS switch me from Wegovy to Mounjaro or vice versa?
Possibly, depending on your response and your specialist service's protocols. If one medication isn't working or causes side effects, your prescriber may consider alternatives. Any change must be managed by your healthcare provider.
How do I access Mounjaro or Wegovy on the NHS in the UK?
Request a referral to your regional tier 3 or 4 specialist weight management service from your GP. Availability and waiting times vary significantly by area. Private prescription is available through UK-licensed online prescribers if NHS waiting lists are lengthy.
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.