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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Mounjaro vs Wegovy: Price, Dosing, and Effectiveness in the UK
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription weight loss injections available in the UK, but they differ in mechanism, dosing schedules, cost, and clinical trial outcomes. Understanding the differences between these two GLP-1 (and dual GLP-1/GIP) medications can help you and your prescriber decide which might be more suitable for your individual situation. This guide compares both injections side-by-side across pricing, effectiveness, and access routes. Use our free GLP-1 weight loss calculator to explore projected outcomes at different doses for either medication.
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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.
Clinical Trial Results and Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways, which is distinct from Wegovy's single mechanism. In the SURMOUNT-1 clinical trial, Mounjaro achieved average weight loss of approximately 15% body weight at 5 mg, 19.5% at 10 mg, and 20.9% at 15 mg over 72 weeks alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1-only receptor agonist. The STEP-1 clinical trial showed average weight loss of approximately 14.9% body weight at the maximum dose (2.4 mg) over 68 weeks with similar lifestyle support. Both medications require ongoing clinical assessment and prescriber monitoring. Individual results vary significantly — these are trial averages, not assured outcomes. Your prescriber will assess which mechanism and dosing profile suits your health needs and previous treatment response.
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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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UK Pricing, Access, and Practical Differences
Both Mounjaro and Wegovy are prescription-only medicines requiring clinical assessment before dispensing in the UK. Private costs typically range from £129–£320 per month depending on dose and provider — Mounjaro costs are generally comparable to Wegovy at similar clinical dose levels, though pricing varies by pharmacy. NHS access is through specialist tier 3 weight management services; availability varies significantly by region and waiting lists can be lengthy.
Dosing schedules differ: Mounjaro starts at 2.5 mg and escalates to a maximum of 15 mg once weekly, while Wegovy starts at 0.25 mg and escalates to 2.4 mg once weekly. Both are once-weekly injections using pre-filled pens. Neither medication assures weight loss — results depend on adherence, lifestyle changes, and individual metabolic response. Your GP or licensed prescriber will assess your eligibility and suitability for either medication based on your BMI, health conditions, and medical history.
- 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 Mounjaro and Wegovy mechanism?
Mounjaro (tirzepatide) is a dual GIP+GLP-1 receptor agonist — it activates two hormone pathways — while Wegovy (semaglutide) is a GLP-1-only agonist. This dual action in Mounjaro may contribute to slightly higher average weight loss in clinical trials, though individual results vary significantly and both are effective.
Which is cheaper in the UK, Mounjaro or Wegovy?
Pricing is comparable between Mounjaro and Wegovy in UK private prescribing, typically £129–£320 monthly depending on dose and provider. Exact cost varies by pharmacy and dose level. NHS access for both is through specialist services with regional variation. Always check current prices with your prescriber or pharmacy.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications must be managed by your prescriber — there is no official conversion chart. An approximate equivalence exists (e.g., Wegovy 2.4 mg ≈ Mounjaro 15 mg clinically), but any switch requires medical supervision, dose adjustment, and clinical reassessment of tolerance and response.
Do I need to be on the NHS or can I access these privately?
Both medications are available through NHS specialist weight management services (tier 3) or via private prescription following an online clinical assessment with a UK-licensed prescriber. NHS access has longer waiting lists; private access is faster but requires out-of-pocket cost.
How do the clinical trial weight loss results compare?
SURMOUNT-1 (Mounjaro) showed ~20.9% average weight loss at maximum dose over 72 weeks. STEP-1 (Wegovy) showed ~14.9% average weight loss at maximum dose over 68 weeks. Both used reduced-calorie diets and exercise. Trial durations and populations differed slightly, so direct comparison requires prescriber guidance.
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