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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Getting Mounjaro on the NHS vs Wegovy
If you're exploring weight management options through the NHS, you may have heard about both Mounjaro (tirzepatide) and Wegovy (semaglutide). Both are prescription-only GLP-1-based weight loss injections licensed in the UK, but they work differently and have different availability. This guide explains the key differences, eligibility criteria, and how to access each through NHS specialist services. Use our free BMI calculator to check whether you may qualify for NHS treatment first.
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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 Mounjaro and Wegovy Differ — Trial Data and Mechanisms
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways. The SURMOUNT-1 clinical trial showed participants on the maximum 15 mg dose lost an average of 20.9% of their body weight over 72 weeks, alongside diet and activity changes. Individual results vary significantly.
Wegovy (semaglutide) is a single GLP-1 receptor agonist, activating one hormone pathway. The STEP-1 trial demonstrated approximately 14.9% average weight loss at the maximum 2.4 mg dose over 68 weeks, also with dietary and exercise support.
- Mounjaro: dual mechanism, once-weekly 2.5–15 mg injection
- Wegovy: single mechanism, once-weekly 0.25–2.4 mg injection
- Both require minimum 4-week intervals between dose increases
- Both available through NHS tier 3 specialist weight management services
The SURMOUNT trial data suggests a potentially larger average weight loss with Mounjaro, but individual response varies — some people respond better to one 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.
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NHS Access and Individual Suitability — What Your Prescriber Decides
Both Mounjaro and Wegovy are available through NHS specialist tier 3 weight management services, but access varies significantly by region (ICB). You'll need referral from your GP. Regional waiting lists can be lengthy — some areas have waits of several months or longer. A specialist prescriber will assess your individual health history, medications, and suitability for each medication.
Eligibility for both requires: BMI ≥30, or BMI 27–29.9 with weight-related health conditions (type 2 diabetes, hypertension, dyslipidaemia, sleep apnoea, or cardiovascular disease). For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds may apply. Your prescriber will recommend the most appropriate option based on your medical profile, not trial averages. Try our GLP-1 weight loss calculator to explore potential outcomes at different doses.
- 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 get Mounjaro on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is approved for NHS use through specialist tier 3 weight management services. You'll need a GP referral and a clinical assessment by the specialist team. Availability and waiting times vary significantly by region. Not all ICBs offer equal access, so contact your local weight management service for current timelines.
Is Mounjaro better than Wegovy for weight loss?
Clinical trials show Mounjaro may support slightly higher average weight loss (20.9% vs 14.9%), but individual results vary considerably. Some people respond better to one medication than the other. Your prescriber will recommend the most suitable option based on your health history, not trial averages alone.
What's the difference between Mounjaro and Wegovy mechanisms?
Mounjaro is a dual GIP and GLP-1 receptor agonist (two hormone pathways), while Wegovy is a GLP-1 receptor agonist only (one pathway). The dual mechanism may contribute to Mounjaro's potentially larger average weight loss in trials, but both require lifestyle changes alongside medication use.
How long is the NHS waiting list for Mounjaro?
NHS waiting times vary by region and current demand. Some areas have waits of several months; others may be longer. Contact your local NHS weight management service directly after GP referral to get a realistic timeline for your area. Private prescribing options are available if NHS waiting times are prohibitive.
Do I need a Mounjaro kwikpen prescription or can my GP prescribe it?
Mounjaro is typically prescribed through NHS tier 3 specialist weight management services, not standard GP practice. Your GP refers you to the specialist service, where a prescriber assesses and initiates treatment if appropriate. This ensures proper monitoring and support throughout your treatment.
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.