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: Cost, Effectiveness & How They Compare in the UK
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections available in the UK, but they work differently and have different costs. Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 agonist only. Costs vary between private providers, and both require a clinical assessment before prescription. Understanding the differences between these medications — including clinical trial results, mechanism of action, and eligibility criteria — can help you make an informed decision about which might be suitable for you, with guidance from a licensed prescriber.
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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 Mounjaro and Wegovy Work Differently
Mounjaro (tirzepatide) activates two hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual mechanism may help reduce appetite, slow gastric emptying, and regulate fat utilisation more effectively than single-pathway medications.
Wegovy (semaglutide) activates the GLP-1 pathway only. Clinical trials showed Wegovy helped participants lose an average of approximately 14.9% of their body weight at the maximum dose over 68 weeks.
In the SURMOUNT-1 trial, Mounjaro at 15 mg showed average weight loss of approximately 20.9% over 72 weeks — though individual results vary significantly. Both medications are most effective when combined with a reduced-calorie diet and increased physical activity. A licensed prescriber will assess which medication is most suitable based on your individual health profile and needs.
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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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Cost, Dosing, and Prescriber Assessment
Private Mounjaro costs typically range from £129–£320 per month depending on dose, whilst Wegovy costs range similarly depending on dose and provider. Mounjaro uses a KwikPen device with doses from 2.5 mg to 15 mg once weekly. Wegovy uses an auto-injection pen with doses from 0.25 mg to 2.4 mg once weekly. Both require a prescription from a UK-licensed prescriber following a clinical assessment. Your GP can refer you to NHS specialist weight management services (tier 3), though waiting times vary by region. Private prescribing is also available without NHS referral if you prefer faster access. Use our free GLP-1 weight loss calculator above to explore potential outcomes, and our BMI calculator to assess your current health status.
- 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 cheaper than Wegovy in the UK?
Cost varies by provider and dose. Both medications typically cost between £129–£320 per month privately. Mounjaro uses larger doses (up to 15 mg), whilst Wegovy's maximum dose is 2.4 mg. Comparison depends on your prescribed dose and chosen provider. Always request current pricing from your prescriber.
Which is more effective — Mounjaro or Wegovy?
Clinical trials showed Mounjaro achieved average weight loss of approximately 20.9% at maximum dose, whilst Wegovy achieved approximately 14.9%. However, individual results vary significantly. Effectiveness depends on your personal response, lifestyle changes, and adherence. Your prescriber will assess which suits you best.
Can I get Mounjaro or Wegovy on the NHS?
Yes, both are available through NHS tier 3 specialist weight management services. However, availability and waiting times vary significantly by region. You'll need a referral from your GP. Private prescribing offers faster access if you prefer not to wait for NHS services.
What's the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 agonist only. The dual mechanism in Mounjaro may provide different appetite-suppressing effects. Both work best alongside a reduced-calorie diet and increased physical activity.
How do I choose between Mounjaro and Wegovy?
A licensed prescriber will assess your health profile, medical history, eligibility, and any contraindications to recommend the most suitable medication. Both require a clinical assessment. Neither medication is "better" — suitability is individual. Your prescriber's assessment is the key to choosing correctly.
Ready to take control of your weight loss journey?
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