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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Monjaro vs Wegovy — Cost and Effectiveness Compared
If you're looking for affordable weight loss injections in the UK, you may be comparing Mounjaro and Wegovy — two prescription-only medications that work in different ways. Both are licensed for weight management in UK adults, and both are available through NHS specialist services or private prescribing. Understanding the key differences between them can help you have a more informed conversation with your GP or prescriber about which option might be suitable for your individual situation.
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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 Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways that help regulate appetite and blood sugar. In the SURMOUNT-1 clinical trial, participants taking the maximum 15 mg dose lost an average of around 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates a single hormone pathway. In the STEP-1 clinical trial, the maximum 2.4 mg dose resulted in an average weight loss of approximately 14.9% of body weight over 68 weeks, also alongside dietary and lifestyle changes.
Important context: these are clinical trial averages. Individual results vary significantly, and weight loss is not assured. Both medications work best when combined with sustainable eating habits and regular physical activity. Use our GLP-1 weight loss calculator to explore estimated weight loss projections at different doses.
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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 Which Might Suit You
Pricing varies between providers and doses. Generally, Mounjaro costs range from around £129–£250 per month on private prescription, while Wegovy typically ranges from £130–£300 monthly, depending on dose and supplier. Costs are lower at starting doses and increase with escalation.
NHS access to both medications is through specialist tier 3 weight management services — referral from your GP is usually required, though waiting lists vary significantly by region. For private access, both require an online clinical assessment confirming you meet eligibility criteria (BMI ≥30, or BMI 27–29.9 with weight-related health conditions). Your prescriber will consider factors including your health history, other medications, and personal preference to recommend the most appropriate option. Both are prescription-only and require ongoing clinical monitoring.
The choice between Mounjaro and Wegovy is not simply about which is "cheaper" — it depends on your individual clinical suitability, which dose you stabilise at, and how you respond. Some people respond better to the dual mechanism of tirzepatide, whilst others achieve good results with semaglutide alone. Your prescriber will assess your medical history, current medications, and health goals to recommend the most suitable option. Calculate your current BMI using our BMI calculator to understand your starting point, and discuss both medications with your GP or a licensed prescriber to explore which fits your circumstances and budget.
- 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?
Pricing varies between private providers and doses. Both typically cost between £129–£300 per month on private prescription. Mounjaro may be cheaper at higher doses where you've stabilised treatment; Wegovy may be cheaper at starting doses. NHS access is free but requires specialist referral and has varying waiting times by region.
Which causes more weight loss — Mounjaro or Wegovy?
In clinical trials, Mounjaro (tirzepatide) showed slightly higher average weight loss (~21% at maximum dose) compared to Wegovy (~15% at maximum dose). However, individual results vary significantly. What works best depends on your personal response, not the average trial outcome. Your prescriber will assess which suits your circumstances.
What's the difference between tirzepatide and semaglutide?
Tirzepatide (Mounjaro) is a dual GIP and GLP-1 receptor agonist activating two hormone pathways. Semaglutide (Wegovy) is a GLP-1 receptor agonist only, activating one pathway. The dual mechanism of tirzepatide may produce stronger effects for some people, but both are effective weight loss medications requiring prescription and clinical assessment.
Can I get Mounjaro or Wegovy free on the NHS in the UK?
Yes, both are available on the NHS through specialist tier 3 weight management services. You typically need a GP referral. However, availability and waiting times vary significantly by region (ICB). Private prescription is available without NHS referral but costs approximately £129–£300 per month depending on dose and provider.
Which weekly weight loss injection should I choose?
The choice depends on your individual health profile, not just cost. Factors include your current BMI, existing health conditions, other medications, and how you respond to each medication. Your GP or a licensed prescriber will assess your suitability and recommend the most appropriate option based on clinical assessment, not price alone.
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.