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 — Complete UK Comparison
Comparing Mounjaro and Wegovy in the UK? Both are prescription-only weight loss injections licensed for adults with obesity or overweight with health conditions, but they work differently and have different costs. This guide explains the key differences between tirzepatide (Mounjaro) and semaglutide (Wegovy), including pricing, mechanisms, clinical trial results, and how to access them. Individual suitability is assessed by a prescriber, and results vary between people. Use our free GLP-1 weight loss calculator to explore potential outcomes with different medications.
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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 Mounjaro and Wegovy Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways in the gut. This dual mechanism may help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. Wegovy (semaglutide) is a GLP-1-only receptor agonist, activating a single pathway. Both slow gastric emptying and help regulate blood sugar, but the dual action of Mounjaro is the key pharmacological difference.
In the SURMOUNT-1 clinical trial, Mounjaro showed an average weight loss of approximately 20.9% of body weight at the maximum 15mg dose over 72 weeks. The STEP-1 trial for Wegovy showed approximately 14.9% average weight loss at the 2.4mg maximum dose over 68 weeks. Both trials included participants following a reduced-calorie diet and increased physical activity. Individual results vary significantly — some people lose more, some less.
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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.
UK Pricing, Doses, and Access
Mounjaro KwikPen pricing in the UK ranges from approximately £130–£320 per month depending on the dose and private provider. Doses escalate weekly from 2.5mg to a maximum of 15mg. Wegovy pricing is typically £150–£300 per month, with doses escalating from 0.25mg to 2.4mg maximum. Both are available through NHS specialist weight management services (with significant regional variation and waiting lists) or via private online prescribing following a clinical assessment. Your GP or a licensed prescriber will assess whether either medication is suitable for you based on your BMI, health conditions, and medical history. Try our free BMI calculator to check where you stand against UK 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.
Is Mounjaro more effective than Wegovy?
Clinical trials showed Mounjaro achieved slightly higher average weight loss (20.9% vs 14.9%), but individual results vary widely. Suitability depends on your personal health profile, not trial averages. A prescriber will assess which is more appropriate for you based on your specific circumstances and medical history.
What's the cost difference between Mounjaro and Wegovy in the UK?
Prices are broadly similar, ranging £130–£320 monthly. Mounjaro may be slightly more expensive at higher doses because the maximum is 15mg versus Wegovy's 2.4mg. Costs vary by provider and dose. Check with your chosen prescriber for exact current pricing.
How long does a Mounjaro KwikPen last?
One KwikPen contains 4 weeks of doses (4 pre-filled injections), so one pen lasts approximately one month. You'll receive a new pen each month during treatment. Storage requirements vary between unopened (refrigerated) and in-use pens.
Can I switch from Mounjaro to Wegovy or vice versa?
Switching between medications must be managed by your prescriber. There is no official conversion chart — approximate equivalences exist (5mg Mounjaro ≈ 0.5mg Wegovy), but any switch requires a clinical decision and prescription adjustment.
Which injection is available through the NHS in the UK?
Both Mounjaro and Wegovy are approved by NICE for NHS use, but access is through tier 3 specialist weight management services. Availability, waiting times, and eligibility vary significantly by region and local NHS Integrated Care Board. Private prescribing offers faster access without NHS referral.
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.