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
What is Mounjaro and How Does It Work in the UK?
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK for adults with obesity or overweight with related health conditions. It works as a dual GIP and GLP-1 receptor agonist—activating two natural hormone pathways to help regulate appetite, reduce food cravings, and support feeling fuller after meals. Unlike single-mechanism medications like Wegovy, Mounjaro targets both pathways, which is why it's distinct in the UK weight management landscape. This guide explains NHS eligibility, how the KwikPen injection works, expected outcomes, and your options for accessing it through NHS or private routes.
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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 and UK Prescribing Guidance
NICE and NHS approval: Mounjaro (tirzepatide) has been approved by NICE for use within NHS specialist tier 3 weight management services in England, Wales, Scotland, and Northern Ireland. It is subject to additional MHRA monitoring (Black Triangle ▼ status), reflecting rigorous safety oversight.
Who is eligible: Adults with a 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, prediabetes, hypertension, abnormal blood fats, sleep apnoea, or cardiovascular disease history) may be eligible.
Ethnicity adjustments: For South Asian, Chinese, Black African, and Black Caribbean adults, the NHS recommends lower BMI thresholds—eligibility may start at BMI 27.5 or above, as these groups face higher disease risk at lower BMI levels.
Tier 3 services: NHS Mounjaro prescriptions are issued through specialist multidisciplinary weight management teams, not standard GP prescriptions. Access varies significantly by region (Integrated Care Board) and availability. Many areas have waiting lists of several months. Calculate your current BMI using our free BMI calculator above to assess your baseline.
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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 Access vs Private Routes in the UK
NHS route: Referral from your GP to a tier 3 specialist weight management service. Assessment typically includes clinical examination, blood tests, and discussion of lifestyle changes. If approved, Mounjaro is supplied through the NHS, though availability and speed of access vary significantly by region. Some areas have long waiting lists.
Private route: Available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. Private access does not require NHS referral and is faster—typically available within 1–2 weeks. Costs vary by dose (starting around £129–£220 per month for lower doses, rising with higher doses). Both routes require a prescription; Mounjaro is never available over-the-counter.
Our free GLP-1 weight loss calculator can help you explore projected weight loss at different Mounjaro doses alongside your current weight.
- 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.
How much weight can you expect to lose on Mounjaro in the UK?
The SURMOUNT-1 clinical trial showed average weight loss of approximately 15–21% of body weight over 72 weeks at maximum dose (15 mg weekly), alongside reduced-calorie diet and increased physical activity. Individual results vary significantly. UK specialist services typically counsel that weight loss is not assured and lifestyle changes are essential for best outcomes.
What is the difference between Mounjaro and Wegovy on the NHS?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Both are NICE-approved for NHS weight management services. Mounjaro starts at 2.5 mg weekly with a maximum of 15 mg; Wegovy starts at 0.25 mg and reaches 2.4 mg. Mounjaro typically shows higher average weight loss in trials, but individual responses differ. Your GP or specialist will assess which is appropriate.
Can you get Mounjaro on the NHS straight from your GP?
No. Standard GP prescription is not available. You must be referred to a specialist tier 3 weight management service by your GP. They assess eligibility and manage prescribing. This differs from private routes, where you can access a prescriber online without NHS referral. Waiting times for NHS tier 3 services vary by region—some areas have significant delays.
What is the KwikPen and how do you use it?
The Mounjaro KwikPen is a pre-filled, easy-to-use injection device. Each pen contains 4 weekly doses. You inject once weekly into your stomach, thigh, or upper arm (rotating injection sites). The needle is very fine and the injection takes seconds. Your prescriber or nurse will train you on injection technique before your first dose.
Is Mounjaro approved by MHRA for weight loss in the UK?
Yes. Mounjaro is MHRA-approved for weight management in UK adults and is subject to additional monitoring (Black Triangle ▼ status), meaning adverse effects are tracked closely and reported to MHRA. NICE has recommended it for use in NHS specialist services. This reflects rigorous regulatory oversight and ongoing safety review.
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.