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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Mounjaro as a Slimming Injection — NHS and UK Context
Mounjaro (tirzepatide) is a prescription-only weekly weight loss injection now available in the UK for eligible adults. Often referred to as a "slimming injection," it's a dual GIP and GLP-1 receptor agonist that may help reduce appetite and support feeling fuller after smaller meals. Access through the NHS is via specialist tier 3 weight management services, though it's also available privately following a clinical assessment. Individual results vary, and the medication works best alongside a reduced-calorie diet and increased physical activity.
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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 Access to Mounjaro and Eligibility Requirements
NHS NICE Approval: Mounjaro (tirzepatide) has been approved by NICE for weight management through NHS specialist services. However, NHS access is limited to tier 3 multidisciplinary weight management teams, not standard GP prescription.
Eligibility Criteria for Mounjaro on the NHS:
- BMI of 30 kg/m² or above, OR BMI of 27–29.9 kg/m² with weight-related health conditions (type 2 diabetes, high blood pressure, cardiovascular disease, obstructive sleep apnoea, or dyslipidaemia)
- South Asian, Chinese, Black African, or Black Caribbean adults may have lower BMI thresholds (starting at BMI 27.5+)
- Age 18 or over
- Commitment to lifestyle changes alongside medication
Access through NHS tier 3 services typically requires GP referral and can involve waiting lists lasting months to years depending on your region. Use our free BMI calculator to check your starting point.
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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 Mounjaro in the UK
NHS Route: Referral to a specialist tier 3 weight management service through your GP. NICE has approved Mounjaro, but NHS availability varies significantly by region and ICB (Integrated Care Board). Many areas have substantial waiting lists due to high demand.
Private Route: Available through GPhC-registered online prescribing services following a clinical assessment. No GP referral needed. Costs typically range from £130–£320 per month depending on dose. Access is faster than NHS routes, though treatment remains prescription-only and requires a licensed UK prescriber to assess suitability. Both routes offer the same medication—eligibility and suitability are assessed individually in both cases.
- 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 is Mounjaro as a slimming injection?
Mounjaro (tirzepatide) is a once-weekly prescription injectable medication that activates GIP and GLP-1 pathways to help regulate appetite and support weight loss. Clinical trials showed average weight loss of 15–21% over 72 weeks alongside dietary and lifestyle changes. It's not insulin and works differently from other weight loss injections like Wegovy.
What are the NHS eligibility criteria for Mounjaro in the UK?
You may be eligible for Mounjaro on the NHS if you have a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure. South Asian, Chinese, Black African, or Black Caribbean adults may qualify at lower BMI thresholds. Access is through NHS tier 3 specialist services, not standard GP prescription.
How long is the NHS waiting list for Mounjaro?
NHS waiting times vary significantly by region. Many tier 3 weight management services have substantial backlogs—waiting lists can range from several months to over a year depending on your local ICB. Contact your local service directly for accurate timescales. Private prescribing offers faster access.
How does the NHS route differ from private prescribing for Mounjaro?
The NHS route requires GP referral to a tier 3 specialist service and may involve waiting. Private prescribing allows you to access a licensed UK prescriber online without NHS referral, typically within days. Both require clinical assessment; private prescribing costs £130–£320/month depending on dose, while NHS access is free but subject to availability and regional variation.
What is the MHRA status of Mounjaro in the UK?
Mounjaro (tirzepatide) is subject to additional MHRA monitoring and carries Black Triangle (▼) status, meaning it's relatively new and the regulator actively monitors safety data. This is standard for new medicines and does not mean it's unsafe—it simply means healthcare professionals and patients should report any suspected side effects to the regulator.
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.