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 Results vs Wegovy — What the Clinical Evidence Shows
Comparing Mounjaro (tirzepatide) and Wegovy (semaglutide) for weight loss? Both are prescription-only GLP-1-based medications licensed in the UK, but they work differently and deliver different average results. The SURMOUNT and STEP clinical trials provide real data on what you might expect. Use our free GLP-1 weight loss calculator above to explore projected outcomes at different doses. Individual results vary considerably, and the right choice depends on your personal health profile, which a GP or prescriber will assess during a clinical consultation.
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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.
Clinical Trial Results — SURMOUNT vs STEP Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist tested in the SURMOUNT-1 trial. At maximum dose (15 mg once weekly), participants lost an average of 20.9% of their body weight over 72 weeks alongside reduced-calorie diet and increased physical activity. At 5 mg, average loss was around 15%; at 10 mg, approximately 19.5%.
Wegovy (semaglutide) is a single GLP-1 agonist tested in the STEP-1 trial. At maximum dose (2.4 mg once weekly), participants lost an average of 14.9% of their body weight over 68 weeks, also with lifestyle changes. Wegovy requires a longer dose titration schedule (5 steps over approximately 20 weeks) compared to Mounjaro's 4-step escalation.
Both medications are given as once-weekly injections using a pre-filled pen. Important: these are clinical trial averages — individual results vary significantly based on adherence, lifestyle changes, and personal metabolism.
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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.
How They Work Differently — Mechanism Matters
The key difference is mechanism. Mounjaro activates two hormone pathways (GIP and GLP-1), while Wegovy activates only GLP-1. This dual action in Mounjaro may explain slightly higher average weight loss in trials, though both medications reduce appetite, slow gastric emptying, and improve satiety. However, mechanism alone doesn't determine which is right for you — your prescriber will assess your medical history, other medications, and individual suitability. Both require UK prescription following a clinical assessment. Access is through NHS specialist weight management services or private online prescribing. Neither medication is suitable for pregnant women, those under 18, or people with certain medical conditions.
- 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 medication causes more weight loss — Mounjaro or Wegovy?
Clinical trials show Mounjaro achieved average weight loss of 20.9% at maximum dose versus Wegovy's 14.9%, but individual results vary significantly. Some people respond better to one than the other. Your prescriber will help choose based on your health profile, not trial averages.
Does Mounjaro work faster than Wegovy?
Mounjaro has a shorter dose escalation (4 weeks per step vs Wegovy's 5 weeks). Both reach effective doses within 4–5 months. Speed of results depends more on your metabolism and lifestyle changes than the medication choice.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, switching is possible and managed by your prescriber. Approximate dose equivalence exists (for example, Wegovy 2.4 mg is roughly equivalent to Mounjaro 10–12 mg), but any switch requires clinical guidance and a new prescription.
Are side effects the same with Mounjaro and Wegovy?
Very similar. Both commonly cause nausea, diarrhoea, vomiting, and constipation. Side effect profiles are comparable, though individual tolerance varies. Both are prescription-only medications with potential serious side effects — your GP should discuss these fully.
How do I know which medication is right for me?
A UK-licensed prescriber will assess your eligibility, medical history, current medications, and personal preferences. Both require BMI ≥30 (or ≥27 with weight-related health conditions) and clinical assessment. Neither is "better" universally — suitability is individual. ```
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.