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
What Is the Age Limit for Mounjaro in the UK?
Mounjaro (tirzepatide) is only approved for adults aged 18 years and over in the UK. There is no upper age limit, though eligibility depends on individual health factors rather than age alone. If you're under 18, Mounjaro is not suitable. Both Mounjaro and Wegovy follow the same age restriction, as neither GLP-1 nor dual GIP/GLP-1 medications have been studied or approved for weight management in children and young people under 18. Your GP or a licensed prescriber will assess whether you meet the clinical eligibility criteria based on your BMI and health profile.
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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.
Mounjaro vs Wegovy: Age Eligibility and Clinical Differences
Both Mounjaro and Wegovy share the same age requirement: adults 18 years and over only. Neither medication is approved for anyone under 18 in the UK, even if they have significant overweight or obesity. This restriction reflects the lack of clinical trial data in younger age groups and the need to protect young people from untested interventions.
The key difference between these medications is their mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways simultaneously, while Wegovy is a GLP-1 receptor agonist only. In clinical trials (SURMOUNT for Mounjaro, STEP for Wegovy), both showed significant weight loss — Mounjaro averaged 15–clinically studied weight loss, and Wegovy approximately 15%. Both require a UK prescription following clinical assessment through NHS tier 3 services or private online prescribing. Individual suitability depends on your health profile, not just age.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Who Can Access These Medications and How Age Affects Eligibility
Adults aged 18+ with a BMI of 30 kg/m² or above (or 27–29.9 with weight-related health conditions) may be eligible. Your age alone doesn't disqualify you — older adults are regularly prescribed both medications successfully. However, your GP or prescriber will assess other factors: existing medical conditions, current medications, kidney and liver function, and gallbladder health.
For young adults (18–25), prescribers may take extra care reviewing suitability, but there is no automatic age-based exclusion. If you're eligible by BMI and health criteria, you can access Mounjaro or Wegovy through NHS specialist weight management services or private online consultation. Use our free BMI calculator to check your personal BMI, and our GLP-1 weight loss calculator to explore potential outcomes with either medication.
- 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 I get Mounjaro if I'm 19 years old?
Yes, if you meet the clinical eligibility criteria (BMI 30+ or 27+ with health conditions). Age 18+ is the only age restriction. Your prescriber will assess your full health profile, not just age. Eligibility is based on health factors, not age alone.
Is there a maximum age for Mounjaro or Wegovy?
No maximum age limit exists for either medication. Older adults can access both Mounjaro and Wegovy if they meet BMI and health criteria. Prescribers assess suitability based on individual health, kidney function, and existing conditions rather than age.
Why are these medications not approved for under-18s?
Mounjaro and Wegovy have not been studied in children or young people under 18. Clinical trials (SURMOUNT and STEP) only included adults 18+. Without safety and efficacy data in younger age groups, neither medication is licensed for use in under-18s. NHS guidelines do not recommend GLP-1 medications for children.
Are Mounjaro and Wegovy approved for the same age group in the UK?
Yes, both are approved for adults aged 18+ only. Both follow the same age restriction despite different mechanisms. If you're ineligible for Mounjaro due to age, you're also ineligible for Wegovy, and vice versa.
How do I check if I'm eligible for Mounjaro at my age?
Use our free BMI calculator to determine your BMI, then contact your GP or a licensed online prescriber for a clinical assessment. Eligibility depends on BMI, weight-related health conditions, and individual health factors — not age. Most adults 18+ who meet BMI criteria can be considered.
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.