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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Is Mounjaro Better Than Wegovy?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections licensed in the UK, but they work differently and produce different results in clinical trials. Neither is objectively "better" — the right choice depends on your individual health profile, medical history, and how you respond to treatment. This guide compares the two directly so you can understand the key differences and discuss options with your GP or prescriber.
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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 How They Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. In the SURMOUNT-1 clinical trial, participants on the maximum 15 mg dose lost an average of approximately 20.9% of their body weight over 72 weeks, alongside dietary changes and increased physical activity. Those on 10 mg lost around 19.5%, and those on 5 mg lost roughly 15%.
Wegovy (semaglutide) is a single GLP-1 receptor agonist. In the STEP-1 clinical trial, participants on the maximum 2.4 mg dose lost an average of approximately 14.9% of their body weight over 68 weeks using the same lifestyle approach. Both showed greater weight loss than placebo, but Mounjaro's dual mechanism produced numerically higher average outcomes in trials.
Important context: These are clinical trial averages with selected participants. Individual results vary significantly based on genetics, adherence, diet, and exercise. Use our GLP-1 weight loss calculator to explore potential ranges for your situation.
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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.
Side Effects, Dosing, and Your Individual Suitability
Both medications share common side effects including nausea, diarrhoea, constipation, and stomach discomfort — though severity varies. Mounjaro requires dose titration from 2.5 mg weekly up to 15 mg maximum; Wegovy escalates from 0.25 mg to 2.4 mg. Neither is inherently "better" for side effects; individual tolerability differs. A prescriber will assess your medical history, current medications, BMI, and any weight-related health conditions to determine which is more suitable for you. Both are prescription-only and require clinical assessment before dispensing. Your GP or a licensed prescriber will consider your specific circumstances — allergies, contraindications, previous medication responses, and health goals.
- 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 causes fewer side effects — Mounjaro or Wegovy?
Both have similar side effect profiles: nausea, diarrhoea, constipation, and stomach pain are most common. Side effect severity varies between individuals regardless of medication. Your prescriber will choose based on your medical history and individual risk factors, not on generalised comparisons.
Is Mounjaro more effective for weight loss than Wegovy?
Clinical trials show Mounjaro produced higher average weight loss (15–21% vs 14.9%), but this reflects trial populations, not assured individual outcomes. Some people respond better to one than the other. A prescriber will discuss trial data and suitability with you personally.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, switching is possible but must be managed by your prescriber. There is no official conversion chart; your prescriber will determine appropriate dosing. Never switch medications without medical guidance.
How do I know which one my GP will prescribe?
Your GP or prescriber assesses your individual health profile, eligibility criteria (BMI and comorbidities), medical history, and medication interactions. Both require a prescription and clinical assessment. Availability also varies by region and NHS tier 3 waiting lists.
Do I need to choose between them, or can my prescriber recommend one?
Your prescriber makes the recommendation based on your medical circumstances. Use our BMI calculator to check your starting point, then discuss eligibility and suitability with your GP. Both are effective; individual fit matters most.
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.