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: A Complete UK Health Guide
Mounjaro is a prescription-only weight management injection licensed in the UK for adults with obesity or overweight with weight-related health conditions. Also known by its active ingredient tirzepatide, Mounjaro is a dual GIP and GLP-1 receptor agonist — meaning it works on two natural hormone pathways to help regulate appetite and support weight loss. This guide explains how Mounjaro works, UK eligibility criteria, NHS access, and how it compares to other weight loss injections like Wegovy. Always consult your GP or a licensed prescriber before considering any weight loss medication.
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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.
NHS Eligibility and Mounjaro in the UK
In the UK, Mounjaro may be prescribed through NHS specialist weight management services (tier 3) or privately through GPhC-registered online pharmacies. NHS eligibility typically requires a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, sleep apnoea, or cardiovascular disease.
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS applies lower BMI thresholds (starting at 27.5 kg/m²) because these groups face higher health risks at lower weights. NICE (National Institute for Health and Care Excellence) has approved tirzepatide for use within NHS specialist weight management services, though availability varies significantly by region. NHS access typically involves a referral from your GP to a specialist tier 3 or tier 4 weight management service, and waiting lists can be lengthy in many areas. Try our free BMI calculator above to check whether you might meet the initial eligibility criteria.
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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.
Mounjaro Doses, Side Effects, and NHS vs Private Access
Mounjaro comes as a pre-filled KwikPen device with doses ranging from 2.5 mg (starting dose) up to 15 mg (maximum maintenance dose). Each dose is given as a once-weekly injection. Common side effects include nausea, diarrhoea, constipation, and stomach pain — many improve as your body adjusts. Use our GLP-1 weight loss calculator to estimate potential weight loss at different doses based on clinical trial data.
NHS access: Available through specialist weight management services; significant waiting lists in many regions. Private access: Available through GPhC-registered online pharmacies following an online clinical assessment; typically faster access but at personal cost (approximately £150–£300+ per month depending on dose). Either route requires a prescription from a UK-licensed prescriber. Your GP can advise which route is best for you.
- 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 Mounjaro the same as Wegovy?
No. Both are GLP-1 medicines for weight management, but Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro starts at a higher dose (2.5 mg) with a maximum of 15 mg. In clinical trials, Mounjaro showed slightly higher average weight loss (~20.9% body weight at maximum dose) compared to Wegovy (~14.9%). Individual results vary significantly.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is available through NHS specialist (tier 3) weight management services following NICE approval. However, availability varies by region and waiting lists can be very long. You'll need a referral from your GP. Private prescribing is faster but not covered by the NHS. Ask your GP about options in your area.
What is tirzepatide and how does it work?
Tirzepatide is the active ingredient in Mounjaro. It's a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways involved in appetite regulation and blood sugar control. This helps reduce hunger, increase feelings of fullness, and slow gastric emptying. It may help you eat less and feel satisfied with smaller meals.
How much weight can I expect to lose on Mounjaro?
Clinical trials showed average weight loss of 15–21% body weight depending on dose over 72 weeks alongside a reduced-calorie diet and physical activity. Individual results vary significantly — some people lose more, some less. Your GP or prescriber can discuss realistic expectations based on your personal health profile.
What are the most common Mounjaro side effects?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain. Many improve within weeks as your body adjusts. Less common side effects include fatigue, dizziness, headache, and injection site reactions. Serious side effects are rare but seek urgent help if you experience severe stomach pain or signs of allergic reaction.
Ready to take control of your weight loss journey?
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