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: Cost, Effectiveness and UK Access
Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are prescription-only weight loss injections licensed in the UK, but they differ in cost, mechanism, and dosing schedules. Understanding these differences helps you and your GP or prescriber decide which might be more suitable for your individual circumstances. Both require a clinical assessment before prescription, and both are used alongside dietary changes and increased physical activity for best results.
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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 They Work and What Clinical Trials Showed
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates one hormone pathway to reduce appetite and support feeling fuller after meals. Clinical STEP trials showed Wegovy helped participants lose an average of approximately 15% of body weight over 68 weeks at the maximum 2.4mg dose, when combined with reduced-calorie diet and physical activity.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways, which may offer a different mechanism. SURMOUNT clinical trials showed tirzepatide helped participants lose an average of 15–21% of body weight over 72 weeks at the maximum 15mg dose, again alongside lifestyle changes. Individual results vary significantly, and neither medication assures specific weight loss outcomes.
In clinical practice, Mounjaro's dual mechanism and higher trial weight loss averages have generated interest, but Wegovy remains well-established and effective for many people. Your prescriber will assess which is more suitable based on your health profile and medical history.
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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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UK Cost, Access Routes and Practical Considerations
Private prescription costs in the UK typically range from £129–£180 per month for Wegovy (dose-dependent) and £140–£320 per month for Mounjaro (dose-dependent). Mounjaro's higher maximum dose and potentially greater weight loss may reflect higher private costs at top doses.
NHS access is through tier 3 specialist weight management services via GP referral. Availability and waiting times vary significantly by region and ICB. Once approved through NHS specialist services, medications are dispensed at standard NHS prescription costs (currently £9.90 per item in England if eligible).
Practical differences: Both are once-weekly injections; Wegovy starts at 0.25mg, Mounjaro at 2.5mg. Mounjaro's KwikPen device and dual mechanism appeal to some, while Wegovy's longer track record and simpler mechanism suit others. A prescriber will discuss suitability, side effects, and injection technique with you.
- 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?
Clinical trials show Mounjaro averaged slightly higher weight loss (15–21% vs 15% body weight), but individual results vary considerably. Both are effective; suitability depends on your health profile. Your prescriber will assess which is appropriate for you following clinical assessment.
Why does Mounjaro cost more than Wegovy in the UK?
Mounjaro's higher maximum dose (15mg vs 2.4mg), dual mechanism, and potentially greater average weight loss in trials may reflect higher private costs. Pricing also varies by provider and dose. NHS costs are standardised at £9.90 per item for eligible patients.
Can I switch from Wegovy to Mounjaro or vice versa?
Switches between medications must be managed by your prescriber. There is no official conversion chart, though approximate dose equivalences exist (0.5mg Wegovy ≈ 5mg Mounjaro). Any change requires clinical reassessment and guidance.
How do I access Wegovy or Mounjaro on the NHS in the UK?
Request a referral from your GP to a tier 3 specialist weight management service. Eligibility requires BMI ≥30 (or ≥27 with weight-related health conditions). Availability and waiting times vary by region. Private access is faster through online consultations with UK-licensed prescribers.
Which injection is better for me — Wegovy or Mounjaro?
Neither is universally "better" — both are effective, and choice depends on your health history, side effect tolerance, cost, and prescriber recommendation. Use our free GLP-1 weight loss calculator to estimate potential outcomes, then discuss suitability with your GP or prescriber during clinical assessment.
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.