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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Starting Mounjaro in the UK: NHS Guide
Starting Mounjaro (tirzepatide) in the UK involves understanding NHS eligibility criteria, NICE approval status, and whether you'll access treatment through NHS specialist weight management services or private prescription. This guide explains the NHS pathway, tier 3 services, eligibility requirements, and what to expect when beginning tirzepatide treatment.
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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.
NHS Eligibility and Mounjaro Access in the UK
NICE Approval: Mounjaro (tirzepatide) has been approved by NICE for use within NHS specialist weight management services. However, NHS access is limited to tier 3 and tier 4 specialist services — not standard GP prescription.
Eligibility criteria for NHS Mounjaro:
- BMI of 30 kg/m² or above, OR
- BMI of 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, hypertension, dyslipidaemia, sleep apnoea, or cardiovascular disease history)
- For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds may apply from 27.5 kg/m²
Access requires referral from your GP to a tier 3 specialist weight management service. Regional availability varies significantly — waiting lists can extend several months in many areas. Use our free BMI calculator to check where your weight sits against NHS thresholds.
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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.
NHS vs Private Routes for Starting Mounjaro
NHS route: Referral through your GP to a specialist weight management service (tier 3). Prescription issued by the specialist team. Free on the NHS if prescribed through this route. Availability depends on your ICB (Integrated Care Board) region and can involve extended waiting times.
Private route: Consultation with a UK-licensed prescriber through a GPhC-registered pharmacy. Prescription issued if clinically appropriate following assessment. Available without NHS referral. Costs typically range from £129–£320 per month depending on dose. Private access is faster but you pay directly.
Whichever route you choose, a prescriber will assess your medical history, current medications, and suitability before starting. Try our free GLP-1 weight loss calculator to explore potential outcomes at different Mounjaro doses.
- 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.
What's the difference between Mounjaro and Wegovy when starting treatment?
Both are once-weekly injections for weight management. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is GLP-1 only. Mounjaro may support slightly higher average weight loss in trials (15–21% vs 15%). Starting doses differ: Mounjaro starts at 2.5 mg, Wegovy at 0.25 mg. Your prescriber will recommend which is appropriate for you.
Can my GP prescribe Mounjaro directly, or do I need a specialist?
In most areas, your GP will refer you to an NHS tier 3 specialist weight management service, which will then prescribe Mounjaro if you're eligible. Standard GP practices do not hold Mounjaro stock. Private online prescribers can issue prescriptions directly without NHS referral, though you'll pay privately.
How long does it take to start Mounjaro after being referred?
NHS waiting times vary significantly by region. Some areas have waits of 6–12 months; others longer. Private routes are typically faster — prescription issued within days of assessment. If NHS waiting times are lengthy in your area, private prescription may be an alternative option to discuss with your GP.
What should I avoid when starting Mounjaro?
Mounjaro may reduce absorption of oral contraceptives — use a barrier method or non-oral contraceptive for 4 weeks after starting and 4 weeks after each dose increase. Inform your prescriber of all medications. Avoid missed doses; if you miss by more than 4 days, skip and resume normal schedule. Do not freeze the pen.
Will I need blood tests before starting Mounjaro?
Yes. Your prescriber will likely check blood glucose, kidney function, and liver function before starting. If you have type 2 diabetes or take diabetes medication, additional monitoring may be needed. Your prescriber will explain what tests are required based on your health history. ```
Ready to take control of your weight loss journey?
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