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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Compound Mounjaro vs Wegovy — UK Comparison
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both prescription-only weight management injections available in the UK, but they work differently and have different clinical trial results. Understanding the key differences can help you and your GP or prescriber make an informed decision about which medication may 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.
How Mounjaro and Wegovy Work — Mechanism Differences
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates one natural hormone pathway. It signals to your brain that you are full, slows how quickly food leaves your stomach, and helps regulate blood sugar. Wegovy is taken as a once-weekly injection, with doses ranging from 0.25 mg up to a maximum of 2.4 mg.
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 compared to GLP-1 alone. Mounjaro is also a once-weekly injection, with doses ranging from 2.5 mg up to 15 mg. In UK prescription practice, the tirzepatide compound formulation is what's available through both NHS and private prescribing pathways.
Both medications work alongside a reduced-calorie diet and increased physical activity — they are not standalone treatments.
Clinically BackedWeight Loss
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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.
Clinical Trial Results — What the Evidence Shows
The SURMOUNT-1 trial (Mounjaro) showed average weight loss of approximately 15% at 5 mg, 19.5% at 10 mg, and 20.9% at 15 mg over 72 weeks. The STEP-1 trial (Wegovy) showed average weight loss of approximately 14.9% at 2.4 mg over 68 weeks. Both studies involved participants following a reduced-calorie diet and exercise programme.
Important context: These are clinical trial averages — individual results vary significantly. Some people lose more, some less. Trial participants were carefully selected, so real-world results may differ. Your prescriber will assess which medication suits your individual health profile, medical history, and weight loss 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.
Is compound Mounjaro better than Wegovy?
No medication is universally "better" — it depends on individual circumstances. Mounjaro's dual mechanism may suit some people, whilst Wegovy's single-pathway approach works well for others. Your GP or prescriber will assess your medical history, other medications, and individual suitability. Both are prescription-only and require clinical assessment.
Can I switch from Wegovy to compound Mounjaro?
Yes, but only under prescriber guidance. There is no official established conversion chart between the two medications. Any switch must be managed by your healthcare provider, who will assess whether a change is appropriate and adjust your starting dose accordingly. Never stop one medication and start another without medical supervision.
What's the difference between Mounjaro and Ozempic?
Mounjaro (tirzepatide) and Ozempic (semaglutide) are different medications. Ozempic is approved for type 2 diabetes (up to 2 mg dose) and is not licensed for weight loss in the UK. Mounjaro is specifically licensed for weight management at higher doses (up to 15 mg). Using Ozempic for weight loss would be off-label use. Always use the medication licensed for your specific indication.
How do I know which weight loss injection is right for me?
Only a licensed prescriber can assess your suitability following a clinical assessment. They will review your BMI, health conditions, current medications, family history, and weight loss goals. Use our GLP-1 weight loss calculator to estimate potential results, and our BMI calculator to check your current health category — then discuss your options with your GP or private prescriber.
Are compound Mounjaro and Wegovy available on the NHS in the UK?
Both are available through NHS specialist tier 3 weight management services, but access varies significantly by region and waiting lists can be lengthy. Private prescribing is available through GPhC-registered online pharmacies following an online consultation with a UK-licensed prescriber. Your GP can discuss which pathway is most appropriate for you.
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.