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 — Comparing Price and Suitability in the UK
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but they work differently and may vary in price depending on your prescriber. This guide explains the key differences so you can understand which might be more suitable for your situation — though your prescriber will make the final recommendation based on your individual health. Use our free GLP-1 weight loss calculator to estimate potential results with either medication, and our BMI calculator to check your eligibility starting point.
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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 — The Mechanism Difference
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. This means it activates two natural hormone pathways simultaneously — both glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). This dual mechanism may help regulate appetite more comprehensively and support feeling fuller after meals.
Wegovy (semaglutide) is a single GLP-1 receptor agonist, activating only the GLP-1 pathway. This single mechanism is also effective for weight management, though it works through one hormone pathway rather than two.
In the SURMOUNT-1 clinical trial, Mounjaro at maximum dose (15 mg weekly) showed average weight loss of approximately 20.9% of body weight. In the STEP-1 trial, Wegovy at maximum dose (2.4 mg weekly) showed average weight loss of approximately 14.9%. However, individual results vary significantly, and the right medication depends on your personal health profile, not trial averages.
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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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Price Comparison and What Affects Cost
NHS access: Both medications may be available through NHS specialist weight management services (tier 3), though availability varies by region and both have restricted eligibility criteria. NHS prescriptions, if available, have standard prescription charges (currently £9.65 per item in England for those not exempt).
Private access: Mounjaro typically costs £129–£200 per month depending on dose, while Wegovy typically costs £149–£249 per month. These are approximate ranges and vary by prescriber and pharmacy. Both require an initial private consultation (usually £30–£75). Your prescriber will assess which is clinically appropriate for you — the cheaper option is not necessarily the right choice. Use our BMI calculator above to check your starting point, and discuss cost alongside clinical suitability with your prescriber.
- 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?
Mounjaro is often slightly cheaper at comparable doses (around £129–£200/month), while Wegovy typically ranges from £149–£249/month privately. However, costs vary by prescriber and dose. NHS prices are the same (standard prescription charge) if available through your local service. Always consider clinical suitability alongside cost.
Which medication works better for weight loss?
SURMOUNT trial data shows Mounjaro average loss of ~21% body weight, while STEP trial data shows Wegovy average loss of ~15%. However, individual results vary widely. Your prescriber will recommend based on your personal health profile, not averages. What works best for one person may be different for another.
Can I switch from Wegovy to Mounjaro if I'm not seeing results?
Possibly, but only under your prescriber's guidance. There is no official conversion chart between medications — any switch requires a new assessment and prescription. You cannot self-switch or buy one medication if prescribed the other. Discuss with your prescriber if you feel results aren't meeting expectations.
How do I get the best price on Mounjaro or Wegovy in the UK?
Compare prices across GPhC-registered private prescribers — costs vary. Check whether your local NHS weight management service can prescribe (eligibility and availability vary). Ask about loyalty schemes or bulk discounts. Always use a registered prescriber; unregistered sources pose serious safety risks.
Are both medicines available on the NHS?
Both Mounjaro and Wegovy are licensed in the UK and NICE-approved for specialist NHS use, but availability is limited. Access is through tier 3 specialist weight management services, not standard GP prescription. Waiting lists vary significantly by region. Your GP can refer you if you meet local eligibility criteria.
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.