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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What's the New Rule for Mounjaro in the UK?
Mounjaro (tirzepatide) now has clearer NHS approval pathways in the UK following NICE guidance updates. The "new rule" refers to updated eligibility criteria and prescribing frameworks that determine who can access this weight loss injection through the NHS or privately. Understanding these rules—including BMI thresholds, eligibility criteria, and the difference between NHS and private routes—is essential if you're considering this prescription medication. This guide explains what's changed and how to check if you might be eligible.
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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.
NHS Eligibility Criteria and Prescribing Framework
NICE has approved tirzepatide (Mounjaro) for use within NHS specialist weight management services. The current UK eligibility framework includes:
- Adults with a BMI of 30 kg/m² or above, OR
- Adults with a BMI of 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, high blood pressure, high cholesterol, sleep apnoea, or cardiovascular disease)
- For South Asian, Chinese, Black African, or Black Caribbean adults: lower thresholds may apply (BMI 27.5 and above)
Access is through tier 3 specialist weight management services, not standard GP prescription. Your GP must refer you to a specialist service in your area, which then conducts a full assessment. Unlike private routes using online prescribers, NHS access requires this structured referral pathway. The prescriber will review your full medical history, check for contraindications, and confirm suitability. Clinical trial data from SURMOUNT-1 showed Mounjaro users lost an average of 15–21% of body weight—though individual results vary significantly.
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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: Routes and Differences
NHS route: Free at point of use but requires referral to tier 3 services and can involve waiting lists of months or longer depending on your region (ICB). Availability varies significantly across the UK.
Private route: Available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber. No waiting list but costs approximately £129–£320 per month depending on dose. You can start sooner but pay directly. Both routes require a KwikPen prescription and dose titration from 2.5 mg upwards. Use our GLP-1 weight loss calculator to explore potential weight loss projections at different doses, and our BMI calculator to confirm your starting position against NHS thresholds.
- 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.
Does Mounjaro require a prescription in the UK?
Yes. Mounjaro (tirzepatide) is prescription-only in the UK and cannot be purchased without a valid prescription from a licensed prescriber. Both NHS and private access require clinical assessment and a prescription before any medication is dispensed.
What's the difference between the "new rule" and old Mounjaro eligibility?
NICE's updated approval clarified tier 3 prescribing pathways and confirmed BMI thresholds for both standard and South Asian/Black African/Caribbean populations. The core eligibility hasn't changed significantly, but the prescribing framework and ethnicity-adjusted thresholds are now more explicitly defined.
Can my GP prescribe Mounjaro directly on the NHS?
No. Your GP must refer you to a tier 3 specialist weight management service. GPs cannot prescribe Mounjaro directly within the NHS. Private online prescribers can issue prescriptions outside this pathway.
How long does NHS Mounjaro referral typically take?
Waiting times vary by region but often range from 3–12 months or longer depending on your local ICB. Some areas have very long waiting lists. Private prescribing is faster—typically 1–2 weeks from initial assessment to prescription.
Is Mounjaro covered by NHS prescription charges?
Mounjaro is free at point of use for NHS patients once prescribed through tier 3 services. Private Mounjaro incurs a monthly cost. Prescription charges do not apply to medications prescribed through NHS specialist 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.