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 NHS Criteria vs Mounjaro — What's the Difference?
Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are prescription-only weight management injections available in the UK, but they have different mechanisms and eligibility criteria. Understanding the differences can help you and your GP decide which might be more suitable for you. Both require a clinical assessment before prescription, and both are used alongside dietary changes and increased physical activity. This guide compares the key differences to help you understand what NHS specialists consider when recommending one over the other.
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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.
How Wegovy and Mounjaro Work — and Why It Matters
Wegovy (semaglutide) is a GLP-1 receptor agonist — it works by activating one natural hormone pathway in the body. This single mechanism helps reduce appetite, increase feelings of fullness, and slow how quickly food leaves the stomach.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways simultaneously. This dual action may provide more comprehensive appetite suppression and metabolic support, though individual responses vary.
In clinical trials, SURMOUNT data showed Mounjaro achieved average weight loss of approximately 15–21% body weight, while STEP trial data showed Wegovy achieved approximately clinically studied weight loss. However, these are trial averages — individual results vary significantly based on dose, lifestyle adherence, and personal metabolism.
- Wegovy: GLP-1 mechanism only; maximum dose 2.4 mg once weekly
- Mounjaro: GIP + GLP-1 mechanism; maximum dose 15 mg once weekly
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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
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NHS Eligibility and Prescriber Decision
Both Wegovy and Mounjaro have the same basic NHS eligibility criteria: adults with a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions (type 2 diabetes, prediabetes, high blood pressure, sleep apnoea, or cardiovascular disease). For South Asian, Chinese, Black African, and Black Caribbean adults, lower BMI thresholds (27.5+) may apply.
The choice between them isn't based on eligibility alone — it depends on individual factors your prescriber assesses: medical history, other medications, tolerability of side effects, and previous responses to similar treatments. Use our free GLP-1 weight loss calculator to explore projected outcomes, and our BMI calculator to understand your personal starting point. Your GP or specialist will recommend the most appropriate option for your specific circumstances.
- 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 GLP-1 receptor agonist (single mechanism), while Mounjaro is a dual GIP and GLP-1 receptor agonist (two mechanisms). Both are effective for weight loss, but they work slightly differently. Clinical trials showed both achieve significant weight loss — approximately 15% on average — though individual results vary. Your prescriber will recommend the most suitable option based on your health profile.
Can I get Wegovy on the NHS?
Wegovy can be prescribed through NHS specialist weight management services (tier 3 or 4), but access varies significantly by region. Many areas have lengthy waiting lists. Alternatively, Wegovy is available privately through a UK-licensed prescriber following an online clinical assessment. Private costs typically range from £129–£320 per month depending on dose.
What are the NHS eligibility criteria for both medications?
Both require a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions (type 2 diabetes, prediabetes, hypertension, sleep apnoea, or cardiovascular disease). For South Asian, Chinese, Black African, and Black Caribbean adults, the threshold is BMI 27.5 or above. Age must be 18 or over, and you cannot be pregnant or breastfeeding.
Which medication causes fewer side effects?
Both Wegovy and Mounjaro commonly cause nausea, diarrhoea, constipation, and stomach discomfort, particularly in the first few weeks. Side effect profiles are similar overall. Individual tolerance varies — some people tolerate one better than the other. Your prescriber can discuss which might suit you better based on any previous medication experiences.
How do I access these medications in the UK?
Through NHS specialist services: referral from your GP to a tier 3 weight management service (availability and waiting times vary). Through private prescribing: online consultation with a UK-licensed prescriber, prescription issued if eligible, dispensed by a GPhC-registered pharmacy. Both routes require a clinical assessment to confirm suitability.
Ready to take control of your weight loss journey?
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