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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Taking Mounjaro in the UK — What You Need to Know
Taking Mounjaro (tirzepatide) in the UK requires a prescription following a clinical assessment of your weight, health, and eligibility. This guide explains how to access Mounjaro through both NHS specialist services and private prescribers, how to use the KwikPen injection correctly, and what to expect during treatment. Whether you're considering this GLP-1 and GIP receptor agonist or already taking it, understanding the practical and medical aspects helps you get the most from treatment alongside lifestyle changes.
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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.
How to Access Mounjaro in the UK — NHS vs Private Routes
NHS access to Mounjaro: NICE has approved tirzepatide (Mounjaro) for use within NHS specialist tier 3 and tier 4 weight management services. You cannot get Mounjaro directly from your GP; you must be referred to a specialist weight management service, usually by your GP. Eligibility typically requires a BMI of 30 kg/m² or above, or BMI 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. South Asian, Chinese, Black African, or Black Caribbean adults may be eligible at lower BMI thresholds. NHS waiting lists for specialist services vary significantly by region — some areas have waiting times of many months.
Private access: You can obtain Mounjaro through a GPhC-registered online prescriber without an NHS referral. This requires an online consultation where a UK-licensed prescriber assesses your suitability. If approved, a prescription is issued and dispensed by a registered pharmacy. Private treatment is faster but costs range from approximately £130–£320 per month depending on the dose you're taking.
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.
Using Mounjaro — The KwikPen, Doses, and What to Expect
Mounjaro comes as a pre-filled KwikPen device delivering once-weekly injections. Doses start at 2.5 mg and increase gradually — you typically stay on each dose for at least 4 weeks before escalating, reaching a maximum of 15 mg per week. You inject into your stomach, upper thigh, or upper arm, rotating sites each week. Common side effects include nausea, diarrhoea, and stomach pain, especially in the first few weeks; these often improve as your body adjusts. In clinical trials, people taking Mounjaro lost an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly. Always combine treatment with a reduced-calorie diet and increased physical activity for best results.
- 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.
Do I need a prescription to take Mounjaro in the UK?
Yes, Mounjaro is prescription-only in the UK. You need a prescription from either an NHS specialist weight management service or a private UK-licensed prescriber. It is not available over-the-counter or without clinical assessment.
How long does it take to get Mounjaro on the NHS?
NHS waiting times vary significantly by region. Some areas have waits of 6–12 months or longer. If you need access faster, many people choose private prescribing, which typically provides a prescription within days if approved.
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro starts at 2.5 mg and goes up to 15 mg weekly; Wegovy starts at 0.25 mg and reaches 2.4 mg weekly. Clinical trials showed Mounjaro achieved slightly higher average weight loss (20.9% vs 14.9%), but individual results vary.
Can I use my BMI to check if I'm eligible for Mounjaro?
Your BMI is a starting point. Use our free BMI calculator above to check your BMI, but NHS eligibility also depends on weight-related health conditions and whether you've tried other lifestyle approaches. A healthcare professional will assess your full medical history.
What happens if I miss a Mounjaro injection?
If you miss a dose, take it within 4 days of the scheduled date and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and take your next one on the usual day. Never take a double dose, and maintain at least 72 hours between injections.
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.