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
How Old Do You Have To Be To Take Mounjaro?
You must be at least 18 years old to take Mounjaro in the UK. Mounjaro (tirzepatide) is a prescription-only weight management injection not approved for anyone under 18. This page covers UK eligibility requirements, whether you qualify based on age and BMI, and how to access Mounjaro through the NHS or private prescription routes. Understanding your options helps you plan your weight management journey effectively.
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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 Age & Eligibility Requirements in the UK
Age requirement: You must be 18 years or older. There is no upper age limit, though Mounjaro suitability is assessed individually.
BMI eligibility: In addition to being an adult, you'll need a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, prediabetes, high blood pressure, abnormal cholesterol, sleep apnoea, or cardiovascular disease history).
Ethnicity-adjusted thresholds: If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply—eligibility can start at BMI 27.5 or above. Use our free BMI calculator above to check your personal BMI instantly.
Other exclusions: You cannot take Mounjaro if you're pregnant, planning pregnancy, or breastfeeding. A severe allergy to tirzepatide or any ingredients also excludes you.
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.
NHS vs Private Access: Cost & Availability in the UK
NHS access: Through specialist tier 3 weight management services—requires GP referral. NICE has approved tirzepatide (Mounjaro) for NHS use, but availability varies significantly by region and waiting lists can be lengthy (often 6+ months in many areas).
Private prescription: Available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. Costs typically range from £150–£320 per month depending on your dose and provider, with the Mounjaro KwikPen containing four weekly injections per pack.
Next steps: If you're 18+, meet the BMI criteria, and want to explore options, speak to your GP about NHS referral or consult a private prescriber. Either route will involve a clinical assessment to confirm Mounjaro is suitable for you. Track your progress with our free progress tracker once you've started treatment.
- 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 you get Mounjaro on the NHS if you're under 25?
Yes, if you're 18 or older and meet the BMI and health criteria. Age alone doesn't disqualify you. However, NHS access is through specialist weight management services, not routine GP prescription. Waiting times for NHS specialist services vary widely by region—sometimes 6–12 months or longer. Private prescription routes may be faster.
What's the difference between Mounjaro and Wegovy in terms of age requirements?
Both require you to be 18 or older in the UK. Both are prescription-only weight management injections. Wegovy is a GLP-1 agonist; Mounjaro is a dual GIP/GLP-1 agonist. Eligibility criteria (BMI thresholds, weight-related conditions) are the same. Clinical trial data shows Mounjaro achieved average weight loss of approximately 15–21% body weight versus Wegovy's approximately 15%, though individual results vary.
Do I need to be 18 to get a private Mounjaro prescription?
Yes, you must be at least 18 years old for any Mounjaro prescription in the UK—NHS or private. Private online prescribers will verify your age and conduct a clinical assessment to confirm Mounjaro is safe and appropriate for you. This assessment covers your medical history, current medications, and weight-related health conditions.
Is there an age limit for Mounjaro—can older adults take it?
There is no upper age limit for Mounjaro in the UK. Suitability is assessed individually, regardless of age. Older adults can take Mounjaro if they meet BMI criteria and have no contraindications. A prescriber will assess whether it's appropriate based on your overall health, not your age alone.
How long does the private prescription process take if I'm eligible?
Online private consultations typically take 24–48 hours for a decision. If approved, your prescription is sent to a GPhC-registered pharmacy and dispatched within 1–3 working days. NHS routes are significantly slower due to waiting lists for specialist tier 3 services. Some NHS areas have waiting times exceeding 12 months for initial assessment.
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.