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 — UK Price & Effectiveness Comparison
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections available in the UK, but they differ in cost, mechanism, and trial results. This guide provides a factual comparison of price, doses, and expected outcomes based on clinical evidence, helping you understand what each medication offers. Individual suitability is always determined by a prescriber following a clinical assessment.
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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 How They Work
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways simultaneously. The SURMOUNT-1 clinical trial showed average weight loss of approximately 15% at the 5mg dose, 19.5% at 10mg, and 20.9% at the maximum 15mg dose over 72 weeks, alongside reduced-calorie diet and exercise.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. The STEP-1 clinical trial demonstrated average weight loss of approximately 14.9% body weight at the maximum 2.4mg dose over 68 weeks with the same lifestyle changes.
Both trial results show individual outcomes vary significantly. Mounjaro's dual mechanism may offer slightly greater average weight loss, but Wegovy remains highly effective. Neither medication assures specific results — prescriber assessment determines suitability for each person.
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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 Costs, Doses, and Prescription Access
Pricing varies by dose and provider. Mounjaro typically ranges from £129–£320 monthly depending on your current dose (2.5mg to 15mg). Wegovy costs approximately £129–£250 monthly, with doses scaling from 0.25mg to 2.4mg.
Both are available through NHS specialist tier 3 weight management services or private online prescribing. NHS access requires GP referral and can involve significant waiting lists. Private prescribing via GPhC-registered online services is faster but costs are patient-funded. Your prescriber will assess which medication suits your health profile, weight loss needs, and personal circumstances — this is an individual decision, not determined by cost alone.
Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses for either medication. Both require a valid UK prescription and clinical assessment before dispensing.
- 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 more effective, Mounjaro or Wegovy?
Clinical trials show both are effective. Mounjaro's SURMOUNT trial showed slightly higher average weight loss (20.9% at maximum dose) versus Wegovy's STEP trial (14.9%), but individual results vary widely. Effectiveness depends on your metabolism, lifestyle adherence, and health status — your prescriber will assess which suits you best.
Is Mounjaro cheaper than Wegovy in the UK?
Costs are comparable and vary by provider. Mounjaro ranges roughly £129–£320 monthly; Wegovy £129–£250 monthly depending on dose. Private costs vary significantly between GPhC-registered pharmacies. NHS access is free but availability depends on your local ICB and waiting lists.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro dosing goes up to 15mg weekly; Wegovy to 2.4mg weekly. Both are once-weekly injections. The dual mechanism of Mounjaro activates two hormone pathways, while Wegovy activates one — your prescriber will recommend based on your individual profile.
How long does treatment last with Mounjaro or Wegovy?
Both are typically long-term medications. You continue injections as long as you benefit from them and tolerate the side effects. Treatment is usually ongoing, not a fixed course. If you stop either medication, weight regain is common within months, so most people continue indefinitely if they wish to maintain weight loss.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching is possible and should be managed by your prescriber. Mounjaro 5mg is roughly equivalent to Wegovy 0.5mg, though no official conversion chart exists. Any switch requires clinical assessment and dose adjustment — never attempt to switch independently. Discuss with your prescriber if one medication isn't working well.
Ready to take control of your weight loss journey?
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