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 vs Mounjaro — NHS and UK Eligibility Guide
Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are prescription-only weight loss injections approved in the UK. While NICE has endorsed both medicines for NHS specialist weight management services, they work differently and have distinct eligibility criteria. Understanding how they compare can help you discuss options with your GP or prescriber. Use our GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to assess your starting point for treatment eligibility.
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Calculate Your BMI Instantly
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 Differ — Mechanism and NHS Context
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates one natural hormone pathway to reduce appetite and support fullness after smaller meals. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist — it activates two hormone pathways simultaneously, which may explain its slightly higher average weight loss in trials.
- Wegovy mechanism: GLP-1 only — slows gastric emptying, reduces food cravings, increases satiety signalling
- Mounjaro mechanism: GIP + GLP-1 — dual action may enhance appetite suppression and metabolic support
- STEP trial (Wegovy): Average weight loss ~14.9% body weight at 68 weeks on 2.4 mg alongside lifestyle changes
- SURMOUNT trial (Mounjaro): Average weight loss ~15–21% body weight at 72 weeks, dose-dependent, with similar lifestyle support
Both are once-weekly injections. Individual results vary significantly. NICE approval recognises both as clinically effective options within NHS tier 3 specialist weight management services.
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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 Access and Eligibility for Wegovy in the UK
In the UK, Wegovy access through the NHS is restricted to specialist tier 3 weight management services — you cannot be prescribed it by a standard GP. Eligibility requires referral from your GP and assessment by a multidisciplinary team. NICE guidance states you may be eligible if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease. Lower thresholds apply for South Asian, Chinese, Black African, or Black Caribbean adults (BMI 27.5+). NHS availability varies significantly by region — waiting lists can extend months or years. Private prescription through licensed UK providers offers faster access but requires payment. Use our BMI calculator to check your starting point against NHS eligibility thresholds.
- 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 Wegovy and Mounjaro?
Wegovy (semaglutide) activates GLP-1 pathways only, whilst Mounjaro (tirzepatide) activates both GIP and GLP-1 pathways. The dual mechanism in Mounjaro may result in slightly higher average weight loss in clinical trials, though individual outcomes vary. Both are once-weekly injections licensed in the UK for weight management.
Can I get Wegovy on the NHS?
Wegovy is approved by NICE for NHS use but only through specialist tier 3 weight management services — not standard GP prescriptions. You require a referral from your GP and assessment by a multidisciplinary team. Availability and waiting times vary significantly by region. Private prescription is available faster through licensed UK providers.
What is the NHS eligibility criteria for Wegovy in the UK?
Adults with a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions (type 2 diabetes, hypertension, cardiovascular disease, sleep apnoea) may be eligible. Lower BMI thresholds apply for South Asian, Chinese, Black African, or Black Caribbean adults (starting at BMI 27.5). Your GP assesses suitability.
Is Wegovy the same as semaglutide in Ozempic?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes management (doses up to 2 mg) whilst Wegovy is licensed specifically for weight management (doses up to 2.4 mg). Ozempic is not licensed for weight loss in the UK — using it off-label for weight loss is not recommended. Wegovy is the approved weight management formulation.
How quickly can I access Wegovy through the NHS vs privately?
NHS access can involve waiting several months to years depending on your region's specialist service capacity and referral numbers. Private prescription via licensed UK prescribers typically offers assessment and dispensing within days or weeks, but involves upfront costs. Both routes require a clinical assessment before prescription is issued.
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.