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
Free tracker included with every download this week
Is There An Age Limit For Mounjaro In The UK?
Yes, there is a strict age limit for Mounjaro in the UK. Mounjaro (tirzepatide) is only licensed for use in adults aged 18 years and over. This means it cannot be prescribed to children or teenagers, regardless of their weight or BMI. If you're under 18 and concerned about your weight, your GP can discuss age-appropriate support options with you. Weight management in younger people requires different approaches, and specialist paediatric services are available through the NHS for those who need support.
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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.
UK Age Requirements And NHS Eligibility For Mounjaro
Mounjaro is only available to adults aged 18 and over in the UK. This applies to all routes — both NHS specialist services and private prescribing. Below 18, tirzepatide cannot be prescribed, even if a young person meets other eligibility criteria like having a high BMI.
- Minimum age: 18 years (UK law and MHRA licensing)
- No upper age limit, though individual health assessment applies to all ages
- Eligibility also requires BMI of 30 or above, or 27+ with weight-related health conditions
- Pregnancy and breastfeeding exclude eligibility at any age
- NHS prescription through tier 3 specialist weight management services
- Private prescription following clinical assessment by a UK-licensed prescriber
The reason for the 18+ restriction is that Mounjaro has not been tested or approved for safety and effectiveness in people under 18. Weight management in younger people requires different medical approaches, including paediatric specialist input.
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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.
What To Do If You're Under 18 And Concerned About Weight
If you're under 18 and worried about your weight, speak to your GP, school nurse, or a parent/guardian about support options. The NHS offers weight management support for children and young people through specialist paediatric services, including behavioural support, dietary advice, and family-based interventions.
Your GP can refer you to local services appropriate for your age. Compare your health against NHS BMI centile charts using our free BMI calculator, which shows how your weight compares to healthy ranges for your age group. Younger people benefit from holistic support including physical activity, nutrition education, and emotional wellbeing — these foundations are important before considering any medication-based approaches.
- 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.
Can teenagers take Mounjaro?
No. Mounjaro is only licensed for adults aged 18 and over in the UK. Teenagers cannot be prescribed tirzepatide, even if they have obesity. A GP can discuss alternative weight management approaches suitable for younger people, including lifestyle changes and specialist paediatric services.
Is there an upper age limit for Mounjaro?
No upper age limit exists. Older adults can take Mounjaro if they meet other eligibility criteria (BMI 30+, or 27+ with weight-related conditions) and are assessed as fit for treatment. Individual health checks are important at all ages, but age alone is not a barrier above 18.
What's the difference between Mounjaro and Wegovy age limits in the UK?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) have the same age requirement: 18+ only. Neither GLP-1 nor GIP/GLP-1 medications are licensed for under-18s in the UK. Prescribing follows similar NHS tier 3 pathways and private assessment routes.
Can my GP prescribe Mounjaro privately if I'm under 18?
No. Age restrictions apply across all prescribing routes — NHS and private. The MHRA licensing and UK law both restrict tirzepatide to adults 18+. Private prescribers must follow the same age criteria as NHS services.
What weight support is available for young people under 18?
The NHS provides specialist paediatric weight management services, including behaviour change programmes, dietary guidance, family-based support, and physical activity advice. These are tailored to younger people and available through GP referral to local tier 2/3 paediatric services.
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.