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 in the UK — A Factual Comparison
If you're considering weight loss medication in the UK, you may have heard of both Mounjaro (tirzepatide) and Wegovy (semaglutide). Both are prescription-only injections licensed for weight management, but they work differently and have different cost profiles. This guide compares the two factually — including mechanism, doses, clinical trial data, and how to access each one. Individual suitability is always determined by your prescriber following a clinical assessment. Use our GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to check where you currently stand.
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Calculate Your BMI Instantly
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 — Key Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways. This dual mechanism may help regulate appetite more effectively by working on multiple satiety signals.
Wegovy (semaglutide) is a single GLP-1 receptor agonist — it activates only the GLP-1 hormone pathway, which signals fullness and reduces appetite.
- Mounjaro: dual mechanism (GIP + GLP-1)
- Wegovy: single mechanism (GLP-1 only)
- Both slow gastric emptying (how quickly food leaves the stomach)
- Both require a reduced-calorie diet and increased activity for best results
- Individual response varies considerably between patients
Clinical trial evidence suggests Mounjaro may produce slightly greater average weight loss, though results vary. Both are UK-licensed for weight management in adults with a BMI of 30 or above, or 27+ with weight-related health conditions.
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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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Doses, Clinical Results & Access in the UK
Mounjaro doses: 2.5 mg to 15 mg once weekly. Wegovy doses: 0.25 mg to 2.4 mg once weekly. In the SURMOUNT-1 trial, Mounjaro at 15 mg resulted in average weight loss of approximately 20.9% of body weight over 72 weeks. In the STEP-1 trial, Wegovy at 2.4 mg resulted in average weight loss of approximately 14.9% over 68 weeks — though individual results vary significantly.
Both are available through NHS specialist weight management services (tier 3) or private online prescribing. NHS access requires a GP referral and can involve waiting lists. Private access is available via UK-licensed prescribers following an online assessment. Your prescriber will assess which medication suits your individual health profile, medical history, and preferences. Use our weight loss calculator to explore projected outcomes at different doses.
- 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?
Costs vary by provider and dose. Private prices typically range from £129–£320 per month depending on the medication and dose strength. NHS access is free but availability is limited and varies by region. Your prescriber will discuss cost options during your consultation.
Which causes fewer side effects — Mounjaro or Wegovy?
Both have similar common side effects: nausea, diarrhoea, constipation, and stomach pain. Individual tolerance varies. Nausea often improves as the body adjusts. Serious side effects are rare. Your prescriber will monitor you throughout treatment and adjust if needed.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications should only be done under prescriber guidance. There is no official conversion chart between tirzepatide and semaglutide doses — your prescriber will restart you on an appropriate dose for Mounjaro if switching from Wegovy, or vice versa.
How long does it take to see weight loss results with either injection?
Weight loss typically becomes noticeable after 4–8 weeks at therapeutic doses, though some people see results sooner. Maximum effects are usually seen at 12–16 weeks. Consistency with reduced-calorie diet and physical activity significantly affects results.
Is one injection better for type 2 diabetes?
Mounjaro and Wegovy are both licensed for weight management in the UK. If you have type 2 diabetes, your GP may prefer one over the other based on your individual health profile. Discuss your diabetes management goals with your prescriber — they can advise which medication fits 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.