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: Cost and Effectiveness in the UK
If you're looking for the cheapest weight loss injection in the UK, you'll likely be comparing Mounjaro (tirzepatide) and Wegovy (semaglutide). Both are prescription weight loss injections available through NHS specialist services or private online prescribing. This guide compares their cost, how they work, clinical trial results, and what you need to know to decide which prescription weight loss option might be suitable for you. Always consult your GP or a licensed prescriber about eligibility and suitability.
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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 Effectiveness
Both Mounjaro and Wegovy have demonstrated effectiveness in clinical trials, though results vary by individual. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. In the SURMOUNT-1 trial, participants on the maximum 15mg dose lost an average of approximately 20.9% of their body weight over 72 weeks alongside diet and exercise. Wegovy (semaglutide) is a GLP-1 receptor agonist only. In the STEP-1 trial, participants on the maximum 2.4mg dose lost approximately 14.9% of body weight over 68 weeks with lifestyle changes.
The key difference: Mounjaro targets two hormone pathways while Wegovy targets one. This dual mechanism may contribute to greater average weight loss in trials, though individual responses vary significantly. Both require reduced-calorie diet and increased physical activity for optimal results. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses based on your current weight.
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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.
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UK Pricing, Eligibility, and How to Access
Private cost: Mounjaro typically ranges from £150–£250 per month depending on dose and provider; Wegovy ranges from £129–£199 per month. NHS access: Both medications are available through NHS specialist tier 3 weight management services, though availability varies significantly by region and waiting times can be lengthy.
Eligibility for either medication is similar: BMI of 30+ or BMI 27–29 with weight-related health conditions like type 2 diabetes, hypertension, or sleep apnoea. Lower BMI thresholds apply for South Asian, Black African, or Black Caribbean adults. Your GP or a licensed prescriber will assess suitability based on your medical history. Neither medication is suitable during pregnancy or if you're under 18.
Check your BMI now using our free BMI calculator above to understand where you fall on the healthy weight scale. Remember: both Mounjaro and Wegovy are prescription-only medicines requiring a clinical assessment before prescription. Individual results vary, and both work best alongside a reduced-calorie diet and regular physical activity. Cost should not be the only factor—discuss with your prescriber which mechanism (single GLP-1 vs dual GIP+GLP-1) and administration schedule (daily vs weekly) best suits your lifestyle and health needs.
- 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?
Prices overlap. Mounjaro typically costs £150–£250/month; Wegovy £129–£199/month. Costs vary by dose, provider, and UK region. Lower starting doses of either medication are cheaper than maximum doses. Check with private prescribers or NHS specialist services for current pricing in your area.
Which injection causes more weight loss — Mounjaro or Wegovy?
Clinical trials show Mounjaro (tirzepatide) achieved average weight loss of approximately 20.9% body weight; Wegovy (semaglutide) approximately 14.9%. However, individual results vary significantly based on genetics, adherence, diet, and exercise. Your prescriber can discuss which is more suitable for you.
What's the difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP+GLP-1 receptor agonist (once-weekly, doses 2.5–15mg). Wegovy is GLP-1 only (once-weekly, doses 0.25–2.4mg). Both slow appetite and stomach emptying. The dual mechanism of Mounjaro may offer greater weight loss potential, though side effects are similar. Your GP should advise on which suits you.
Can I get Mounjaro or Wegovy on the NHS?
Yes, both are available through NHS specialist tier 3 weight management services if you meet eligibility criteria (BMI 30+ or 27–29 with comorbidities). Access varies by region—ask your GP about referral. Waiting lists can be lengthy. Private online prescribing offers faster access but at personal cost.
What side effects should I expect from these weight loss injections?
Both commonly cause nausea, diarrhoea, constipation, and stomach pain—especially at higher doses. Side effects often reduce over time. Serious but rare side effects include pancreatitis and gallbladder problems. Your prescriber will discuss all risks. Track your progress and side effects using our free progress tracker to share with your healthcare team.
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.