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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What Is Mounjaro and How Does It Compare to Wegovy?
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK that works differently from Wegovy (semaglutide). While both are once-weekly GLP-1 medications, Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways rather than one. Understanding how they differ — in mechanism, trial results, doses, and eligibility — helps you and your prescriber decide which might be suitable for your individual circumstances. Both require a clinical assessment before prescription.
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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.
Mechanism, Trial Data, and Dose Differences
Mounjaro (tirzepatide) activates both GIP and GLP-1 receptors, targeting two appetite-regulation pathways simultaneously. In the SURMOUNT-1 clinical trial, participants lost an average of 20.9% of their body weight at the maximum 15 mg dose over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) activates only the GLP-1 pathway. The STEP-1 trial showed average weight loss of approximately 14.9% of body weight at the maximum 2.4 mg dose over 68 weeks under the same lifestyle conditions.
Both start at lower doses and increase gradually: Mounjaro ranges from 2.5 mg to 15 mg weekly, whilst Wegovy ranges from 0.25 mg to 2.4 mg weekly. Individual results vary significantly. Use our GLP-1 weight loss calculator above to explore potential outcomes at different doses.
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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.
Eligibility and Prescriber Considerations
Both medications are available in the UK for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure. Access through NHS specialist weight management services involves waiting lists; private prescription is also available following an online clinical assessment with a UK-licensed prescriber.
Your prescriber will assess factors including your medical history, other medications, and personal circumstances to determine suitability. Neither is superior — effectiveness and tolerability vary by individual. Calculate your BMI using our free BMI calculator to check your starting point, and discuss prescription weight loss options with your GP or a registered 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.
What's the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist (activates two hormone pathways), whilst Wegovy activates only GLP-1. This dual mechanism may contribute to Mounjaro's higher average weight loss in trials, though individual results vary. Both are prescription-only and require clinical assessment.
Which achieved better weight loss results in trials?
In clinical trials, Mounjaro at 15 mg showed average weight loss of 20.9% of body weight, whilst Wegovy at 2.4 mg showed approximately 14.9%. However, these are trial averages under controlled conditions with diet and exercise. Your individual results depend on many factors, including adherence and lifestyle.
Can I switch from Wegovy to Mounjaro or vice versa?
Some people do switch between medications, but this must be managed by your prescriber. There is no official established conversion chart between the two — any change requires clinical guidance and potentially an adjustment period to ensure safe dosing.
How long does it take to reach the maximum dose with each?
Mounjaro takes approximately 20–24 weeks to reach 15 mg, increasing by 2.5 mg every 4 weeks. Wegovy takes approximately 16–20 weeks to reach 2.4 mg, increasing gradually over 16 weeks. Your prescriber may adjust timelines based on tolerability.
Are both available on the NHS in the UK?
Both are NICE-approved for NHS use within specialist tier 3 weight management services, but availability varies by region and waiting lists can be lengthy. Private prescription is available through GPhC-registered online pharmacies following an online clinical assessment. Your GP can advise on NHS options in your area.
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.