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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How Much Is the Mounjaro Pen vs Wegovy?
The Mounjaro KwikPen and Wegovy pen are both once-weekly weight management injections available in the UK, but they work differently and cost varies depending on whether you access them via the NHS or privately. Both are prescription-only medicines that require a clinical assessment before being prescribed. Understanding the differences — from mechanism of action to typical costs — helps you have an informed conversation with your GP or prescriber about which option might be suitable for you.
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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.
Mechanism, Doses, and Clinical Trial Results
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways to regulate appetite and support weight loss. Clinical trials (SURMOUNT-1) showed average weight loss of approximately 15–21% of body weight, depending on dose. The Mounjaro KwikPen comes in doses from 2.5 mg to 15 mg, with titration over several weeks.
Wegovy (semaglutide) is a single GLP-1 receptor agonist, activating one hormone pathway. Clinical trials (STEP-1) showed average weight loss of approximately 15% of body weight. Wegovy doses range from 0.25 mg to 2.4 mg, also titrated over several weeks.
- Mounjaro: once-weekly, dual mechanism, higher maximum dose (15 mg)
- Wegovy: once-weekly, single mechanism, lower maximum dose (2.4 mg)
- Both show similar average weight loss in trials, though individual results vary significantly
- Both require a reduced-calorie diet and increased physical activity for best results
Clinically BackedWeight Loss
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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.
Cost, Access, and Prescriber Selection
NHS access: Both medications are NICE-approved for NHS specialist weight management services, but availability varies significantly by region and waiting lists can be lengthy. Your GP can refer you to a tier 3 specialist service, though you may not be offered a choice between the two.
Private access: Costs typically range from £129–£320 per month depending on dose and provider. A private prescriber will assess whether Mounjaro or Wegovy is more appropriate for you based on your health profile, preferences, and any contraindications. Some prescribers may recommend Mounjaro if you've previously tried Wegovy without adequate response, or vice versa.
Both require ongoing prescription and clinical monitoring — they are not one-time treatments.
- 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.
Which is cheaper, Mounjaro or Wegovy?
Costs vary by provider and dose, but both typically range from £129–£320 monthly privately. NHS access is free but availability varies by region. Starting doses (Mounjaro 2.5 mg, Wegovy 0.25 mg) are usually cheaper than maximum doses. Your prescriber will discuss costs during your clinical assessment.
Can I switch from Wegovy to Mounjaro?
Yes, some people do switch between medications if one is not working well or causes unwanted side effects. However, any switch must be managed by your prescriber — never stop one injection and start another without medical guidance. Approximate dose equivalences exist, but they are not official conversions.
Does the NHS prescribe both Mounjaro and Wegovy?
Both are NICE-approved for NHS specialist weight management services. However, NHS availability, prescribing pathways, and choice between the two vary significantly by region and ICB. Your GP can refer you to a specialist service, but you may not be offered a choice of which medication.
What's the difference between Mounjaro's mechanism and Wegovy's?
Mounjaro is a dual GIP and GLP-1 agonist (two hormone pathways), while Wegovy is a single GLP-1 agonist (one pathway). This dual mechanism may theoretically offer different effects on appetite and metabolism, but both show similar average weight loss in clinical trials. Individual response varies.
How do I know which one is right for me?
A licensed prescriber will assess your medical history, current medications, allergies, and health goals during a clinical assessment. They may recommend one over the other based on your individual circumstances. Use our free GLP-1 weight loss calculator above to explore potential weight loss projections, and our BMI calculator to understand your starting point before your consultation.
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.