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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What's the Difference Between Wegovy and Mounjaro?
Wegovy and Mounjaro are both prescription-only weight loss injections available in the UK, but they work differently and have distinct NHS prescribing pathways. Wegovy (semaglutide) is a GLP-1 receptor agonist made by Novo Nordisk, while Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist made by Eli Lilly. Both are licensed for weight management in UK adults with a BMI of 30 or above, or 27 or above with weight-related health conditions. Understanding how they differ can help you discuss options with your GP or a prescriber following a clinical assessment.
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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 Differently
Wegovy (semaglutide) is a GLP-1 agonist — it activates a single hormone pathway to help reduce appetite and increase feelings of fullness. Mounjaro (tirzepatide) works on two pathways simultaneously: GIP and GLP-1, which may offer a dual mechanism. In clinical trials, Mounjaro showed average weight loss of approximately 15–21% of body weight, whilst Wegovy showed approximately clinically studied weight loss. Results vary significantly between individuals.
- Wegovy: 0.25 mg to 2.4 mg once weekly
- Mounjaro: 2.5 mg to 15 mg once weekly
- Both require gradual dose increases over weeks
- Both are self-injected at home using pre-filled pens
Neither is insulin, and both are used alongside a reduced-calorie diet and increased physical activity. Our GLP-1 weight loss calculator can help you estimate potential outcomes at different doses.
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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, NICE Guidance, and Private Routes in the UK
Both Wegovy and Mounjaro are approved by NICE for use in NHS specialist weight management (tier 3) services. However, NHS access varies significantly by region — some ICBs have waiting lists of many months, whilst others may not currently fund either medication. Your GP can refer you to your local tier 3 weight management service. Private access is faster: both are available through GPhC-registered online prescribing services following a clinical assessment, with costs ranging from approximately £129–£320 per month depending on dose. Private prescribers assess eligibility using the same NHS BMI criteria. Use our free BMI calculator to check your eligibility before exploring either route.
- 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?
Mounjaro showed slightly higher average weight loss (15–21% vs 14.9%) in clinical trials, but individual results vary greatly. Neither medication is "more effective" for everyone — response depends on your body, diet, activity level, and how your body responds to each mechanism. Your prescriber can discuss which may suit you best.
Can I switch from Wegovy to Mounjaro on the NHS?
Switching is possible but depends on your NHS tier 3 service's policy. Some services allow switches; others prefer one medication per patient. Discuss with your specialist team. Private prescribers can also manage switches, though any change requires a new clinical assessment and prescription.
Which has fewer side effects, Wegovy or Mounjaro?
Both share similar common side effects: nausea, diarrhoea, constipation, and stomach pain. Mounjaro may cause slightly more nausea at higher doses because it activates two pathways. Individual tolerance varies. Your prescriber will monitor you and adjust doses if needed.
What are the approximate equivalent doses between Wegovy and Mounjaro?
Approximate equivalences are: Wegovy 0.5 mg ≈ Mounjaro 5 mg, Wegovy 1.7 mg ≈ Mounjaro 10 mg, Wegovy 2.4 mg ≈ Mounjaro 15 mg. These are not exact conversions — any switch must be managed by a prescriber who will reassess your needs.
Can I get Wegovy or Mounjaro through my GP without NHS specialist referral?
On the NHS, both are typically prescribed only through tier 3 specialist weight management services after referral. Privately, you can access both directly through online prescribers without an NHS referral, provided you meet eligibility criteria and complete a clinical assessment with a UK-licensed prescriber.
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.