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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Is There An Age Limit For Mounjaro in the UK?
Yes, Mounjaro (tirzepatide) has a strict age limit in the UK: it is only licensed for adults aged 18 years and over. This is a key eligibility requirement that differs from some other medications. If you're interested in whether Mounjaro or alternatives like Wegovy might be suitable for you, understanding the full eligibility criteria — including age, BMI, and health conditions — is essential before any consultation with a prescriber.
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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.
Age Limits: Mounjaro vs Wegovy Eligibility
Mounjaro (tirzepatide) has a minimum age requirement of 18 years. It is not approved for use in adults under 18, including adolescents or teenagers, even if they meet other eligibility criteria like BMI or weight-related health conditions.
Wegovy (semaglutide) also has the same minimum age limit of 18 years in the UK. Both prescription weight management injections are licensed only for adult use.
This age restriction reflects clinical trial data — both the SURMOUNT trial (Mounjaro) and STEP trials (Wegovy) were conducted in adults aged 18 and above. Safety and efficacy in younger populations have not been established, which is why prescribers cannot offer these medications to under-18s regardless of their BMI or other circumstances.
Young people with weight concerns should speak to their GP, who may refer them to specialist paediatric weight management services appropriate for their age group.
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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.
Other Key Eligibility Criteria Beyond Age
While age is a clear-cut requirement, both Mounjaro and Wegovy have additional eligibility criteria assessed on an individual basis. You must have a BMI of 30 kg/m² or above, or BMI of 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, prediabetes, hypertension, or cardiovascular disease.
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply — eligibility may begin at BMI 27.5 or above.
You also cannot be pregnant, planning pregnancy, or breastfeeding. Your prescriber will assess your suitability through a clinical consultation. Use our free BMI calculator above to check your personal BMI, and our GLP-1 weight loss calculator to explore how these medications may work alongside lifestyle changes if you meet the eligibility criteria.
- 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 under 18 get Mounjaro in the UK?
No. Mounjaro is licensed only for adults aged 18 and over in the UK. Teenagers cannot be prescribed Mounjaro, even if they have a high BMI or weight-related health conditions. Young people with weight concerns should speak to their GP about age-appropriate weight management support, which may include referral to specialist paediatric services.
Is the age limit the same for Mounjaro and Wegovy?
Yes. Both Mounjaro (tirzepatide) and Wegovy (semaglutide) have the same minimum age requirement of 18 years in the UK. Neither medication is licensed for use in under-18s, despite differences in their mechanisms (Mounjaro is a dual GIP+GLP-1 agonist; Wegovy is a GLP-1 agonist only).
Why is there an age limit for these weight loss injections?
Both Mounjaro and Wegovy were studied in adults aged 18+ only. Clinical trial data (SURMOUNT for Mounjaro, STEP for Wegovy) did not include younger people, so safety and efficacy in under-18s remain unestablished. Prescribers cannot offer these medications to younger age groups without evidence of their safety in that population.
What are the other main eligibility criteria apart from age?
Beyond age 18+, you typically need a BMI of 30 or above (or 27–29.9 with a weight-related health condition like diabetes or hypertension). You cannot be pregnant, planning pregnancy, or breastfeeding. Your prescriber will assess you individually. Lower BMI thresholds apply to people of South Asian, Chinese, Black African, or Black Caribbean heritage.
Where can I find out if I'm eligible for Mounjaro or Wegovy?
Speak to your GP or contact a UK-licensed prescriber through a GPhC-registered online service. They will review your age, BMI (check ours free above), medical history, and any weight-related conditions to determine suitability. NHS specialist weight management services can also assess eligibility if you're referred through your GP.
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.