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 Injection — NHS and UK Prescribing Guide
Mounjaro (tirzepatide) is a prescription-only weight loss injection now available through NHS specialist weight management services and private prescribing in the UK. This once-weekly injection works by activating GLP-1 and GIP hormone pathways to help reduce appetite and support weight loss alongside diet and physical activity. Understanding NHS eligibility, NICE guidance, and your prescribing options is essential before seeking this 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 NICE Guidance for Mounjaro
NICE (National Institute for Health and Care Excellence) has approved tirzepatide (Mounjaro) for use within NHS specialist weight management services. You may be eligible for NHS Mounjaro if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, or sleep apnoea.
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, eligibility thresholds start at a lower BMI (27.5 or above) because these groups face higher cardiovascular and metabolic risks at lower weights according to NHS guidelines.
- Access is through Tier 3 specialist weight management services — not standard GP prescription
- Your GP can refer you, but availability varies significantly by region and integrated care board (ICB)
- Waiting lists for NHS specialist services can be lengthy in many areas — sometimes several months or longer
- MHRA approval status: Mounjaro carries Black Triangle (▼) monitoring status, meaning it requires additional safety monitoring
Calculate your personal BMI using our free BMI calculator above to check if you fall within the eligibility range for your height and weight.
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 Route for Mounjaro in the UK
NHS access: Free through Tier 3 specialist services following GP referral, but availability is limited and regional. Waiting lists are often several months long. Once approved, you'll receive regular monitoring and support through the NHS service.
Private access: Available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber. This route doesn't require NHS referral and you can access treatment more quickly — typically within days. Costs range from approximately £129–£320 monthly depending on your dose. Our free GLP-1 weight loss calculator can help you estimate what different doses might cost and their projected outcomes. Either route requires a prescription; Mounjaro is never available without clinical assessment.
Whichever route you choose, your prescriber will assess your medical history, current medications, and weight-related health conditions before prescribing. The once-weekly KwikPen injection is administered at home after training. Starting dose is 2.5 mg per week, with gradual increases to a maximum of 15 mg weekly based on tolerance and response. Track your weight loss progress with our free progress tracker to monitor your results alongside diet and activity changes.
- 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 (tirzepatide) free on the NHS in the UK?
Yes, Mounjaro is available free through NHS Tier 3 specialist weight management services if you meet NICE eligibility criteria (BMI ≥30, or ≥27 with comorbidities). Access requires GP referral and availability varies significantly by region. Waiting lists can be very long — sometimes several months — depending on your local integrated care board. Private prescribing is faster but involves costs.
What BMI do I need to be eligible for NHS Mounjaro?
For most UK adults, BMI must be 30 or above, or 27–29.9 if you have weight-related health conditions like type 2 diabetes or high blood pressure. For South Asian, Chinese, Black African, or Black Caribbean adults, thresholds are lower (BMI 27.5+) due to higher metabolic risk at lower weights. Use our BMI calculator to check your personal eligibility.
How does Mounjaro work differently from Wegovy?
Mounjaro (tirzepatide) activates both GIP and GLP-1 hormone pathways, while Wegovy (semaglutide) activates GLP-1 only. Clinical trials suggest Mounjaro may achieve slightly higher average weight loss — around 20.9% of body weight at maximum dose versus approximately 14.9% for Wegovy. Individual results vary significantly. Both require prescription and clinical assessment.
How long does it take to see results with Mounjaro?
Weight loss typically begins within the first 2–4 weeks of starting Mounjaro. Most significant results are seen after 12–16 weeks as your dose increases. The SURMOUNT trial measured weight loss over 72 weeks, showing average results of 15–clinically studied weight loss depending on dose. Results vary between individuals and depend on diet, activity, and consistency.
Can I switch from Wegovy to Mounjaro on the NHS?
Switching between GLP-1 medications is a clinical decision made by your prescriber. The NHS pathway typically involves discussion with your Tier 3 specialist service about whether switching is appropriate based on your response and tolerance. Private prescribers can assess this more flexibly. Any switch must be managed by a qualified prescriber — never self-switch between medications.
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.