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 — Which Is Cheapest in the UK?
If you're looking for the cheapest weight loss injection option in the UK, both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only medicines available through NHS specialist services or private prescribing. Pricing varies significantly between providers and doses. This guide compares both medications factually — mechanism, clinical trial data, and individual suitability — so you can understand what each offers alongside your prescriber's 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 Data and Weight Loss Mechanism
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways. The SURMOUNT-1 clinical trial showed participants on tirzepatide lost an average of 15–21% of their body weight over 72 weeks, depending on dose (5 mg to 15 mg). Individual results vary significantly.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. The STEP-1 clinical trial showed average weight loss of approximately 14.9% body weight at 68 weeks on the maximum 2.4 mg dose. Again, individual results vary.
Both medications work by reducing appetite, supporting fullness after smaller meals, and slowing gastric emptying. The key difference is that Mounjaro's dual mechanism may produce slightly higher average weight loss in trials — but this does not assures better results for any individual.
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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 Pricing, Eligibility, and Prescriber Assessment
Private prescribing costs in the UK range from approximately £129–£320 per month depending on dose and provider. Mounjaro typically costs slightly less at lower doses, but prices converge at higher doses. NHS access is through specialist tier 3 weight management services — availability and waiting times vary significantly by region. Both require a prescription from a UK-licensed prescriber following a clinical assessment. Your GP or a licensed prescriber will assess your BMI, health conditions, medications, and suitability for either medication. Neither medication is "better" universally — individual health factors, tolerability, and response determine which is appropriate for you. Use our free BMI calculator to check where you stand, and discuss options 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.
Is Mounjaro cheaper than Wegovy in the UK?
Pricing varies by provider and dose. Mounjaro may be slightly cheaper at lower doses (2.5–5 mg), but prices are similar at higher doses (10–15 mg vs 2.4 mg maximum for Wegovy). Compare quotes from multiple private prescribers. NHS access requires referral to specialist services and varies by region.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist; Wegovy (semaglutide) is GLP-1 only. SURMOUNT trials showed Mounjaro averaged 15–clinically studied weight loss; STEP trials showed Wegovy averaged 14.9%. Both require prescription. Individual results vary; your prescriber determines suitability.
Which injection works better for weight loss?
Clinical trials show both medications support meaningful weight loss when used alongside diet and activity changes. Mounjaro showed slightly higher average weight loss in trials, but individual response varies considerably. Suitability depends on your health profile, not trial averages. Your prescriber will assess which is appropriate for you.
Can I get Mounjaro or Wegovy on the NHS in the UK?
Yes — both are available through NHS specialist tier 3 weight management services. Access requires GP referral and assessment. Availability and waiting times vary significantly by region and ICB. Private prescribing is faster but requires payment.
How do I know which weight loss injection is right for me?
Neither medication is universally "best." A licensed prescriber will assess your BMI (27+ with health conditions, or 30+), medical history, current medications, tolerability, and health goals. Use our GLP-1 weight loss calculator to explore projected outcomes, then discuss with your prescriber which prescription medicine suits you best.
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.