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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Wegovy Weight Loss Drugs vs Mounjaro: What's the Difference?
Wegovy (semaglutide) and Mounjaro (tirzepatide) are two different weekly weight loss injections licensed in the UK. Both are prescription-only medicines used alongside lifestyle changes to support weight management in eligible adults. While they work through different mechanisms and show different results in clinical trials, choosing between them depends on individual health factors and prescriber assessment. This guide compares how they work, what the evidence shows, and how to access them in the UK.
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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.
How Wegovy and Mounjaro Work Differently
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates one hormone pathway in the body. This single mechanism may help reduce appetite, increase feelings of fullness, and slow how quickly food leaves the stomach.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways simultaneously. This dual mechanism may provide additional appetite suppression and metabolic support.
In the SURMOUNT-1 clinical trial, Mounjaro showed an average weight loss of approximately 20.9% at the highest dose (15 mg) over 72 weeks. In the STEP-1 trial, Wegovy showed average weight loss of approximately 14.9% at its maximum dose (2.4 mg) over 68 weeks. However, individual results vary significantly, and these figures represent averages alongside reduced-calorie diet and increased physical activity.
- Wegovy: once-weekly injection, doses from 0.25 mg to 2.4 mg
- Mounjaro: once-weekly injection, doses from 2.5 mg to 15 mg
- Both require a prescription from a UK-licensed prescriber
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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, Access, and Your GP Decision
Both Wegovy and Mounjaro are available in the UK for adults with a BMI of 30 kg/m² or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to higher health risks at lower weights.
Access in the UK is through NHS specialist tier 3 weight management services (with potentially long waiting lists and regional variation) or through private online prescribing following a clinical assessment. Your GP or a licensed prescriber will assess which medication — if any — is suitable for your individual health, medical history, and weight loss goals. Neither medication assures weight loss; results depend on adherence, diet, and physical activity.
You can use our free GLP-1 weight loss calculator to explore projected weight loss at different doses, and our free BMI calculator to check whether you may be eligible for these treatments.
Both Wegovy and Mounjaro are available in the UK for adults with a BMI of 30 kg/m² or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to higher health risks at lower weights.
Access in the UK is through NHS specialist tier 3 weight management services (with potentially long waiting lists and regional variation) or through private online prescribing following a clinical assessment. Your GP or a licensed prescriber will assess which medication — if any — is suitable for your individual health, medical history, and weight loss goals. Neither medication assures weight loss; results depend on adherence, diet, and physical activity.
You can use our free GLP-1 weight loss calculator to explore projected weight loss at different doses, and our free BMI calculator to check whether you may be eligible for these treatments.
- 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 is more effective — Wegovy or Mounjaro?
Clinical trials show Mounjaro achieved slightly higher average weight loss (approximately 20.9%) compared to Wegovy (approximately 14.9%) in different trials. However, individual results vary significantly. Effectiveness depends on your response, adherence, diet, and exercise. Your prescriber will assess which is most suitable for you based on your health profile.
What are the main side effects of Wegovy?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain. These typically improve over time as your body adjusts. Less common side effects include headache, fatigue, and injection site reactions. Always read the patient information leaflet and discuss concerns with your GP or prescriber.
Can I switch from Wegovy to Mounjaro?
Switching between medications should only be done under medical supervision. While approximate dose equivalences exist (Wegovy 2.4 mg roughly equals Mounjaro 15 mg), there is no official conversion chart. Your prescriber will manage any switch based on your individual response and health needs.
How do I access Wegovy or Mounjaro on the NHS?
Both medications are available through NHS specialist tier 3 weight management services, typically accessed via GP referral. However, availability varies significantly by region and waiting times can be substantial. Your GP can discuss whether referral is appropriate and what services are available in your area.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Ozempic (up to 2 mg) is licensed for type 2 diabetes in the UK, whilst Wegovy (up to 2.4 mg) is licensed specifically for weight management. Using Ozempic for weight loss is off-label. Wegovy is the licensed weight loss version of semaglutide in the UK. ```
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