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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How to Take Mounjaro: UK Dosing, Injection, and Access
Mounjaro (tirzepatide) is a once-weekly injectable prescription medication for weight management in UK adults. This guide explains the correct injection technique, dose titration schedule, storage requirements, and how to access Mounjaro through both NHS specialist services and private prescription routes. Understanding proper administration is essential for safe and effective use alongside lifestyle changes.
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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.
Mounjaro Injection Technique and Dose Schedule
Mounjaro comes as a pre-filled KwikPen device containing a single weekly dose. Injection sites include your stomach (abdomen), upper thigh, or upper arm — rotate the site each week to prevent tissue irritation. Always inject at the same day each week for consistency. The dose titration schedule starts at 2.5 mg for weeks 1–4, increasing by 2.5 mg increments every 4 weeks until reaching your maintenance dose. Maximum dose is 15 mg weekly. Each KwikPen contains 4 doses (4 weeks' supply). Store unopened pens in the fridge at 2–8°C; after first use, keep at room temperature (below 30°C) for up to 30 days. Never freeze Mounjaro. Follow your prescriber's specific instructions — dose progression depends on your individual response and any side effects you experience. If you miss a dose within 4 days, inject as soon as remembered; if more than 4 days have passed, skip to your next scheduled dose.
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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 Access: Cost and How to Get Mounjaro in the UK
NHS route: Mounjaro is available through NICE-approved NHS tier 3 specialist weight management services, typically accessed via GP referral. Availability varies significantly by region and waiting lists can be lengthy. Private route: UK-licensed online prescribers can issue prescriptions following a clinical assessment, dispensed by GPhC-registered pharmacies. Private costs range from approximately £129–£320 per month depending on dose and provider. Both routes require a prescription and eligibility assessment. Use our free BMI calculator to check your starting point, and our GLP-1 weight loss calculator to estimate potential outcomes at different doses. Your prescriber will confirm suitability based on your health profile.
- 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 often do I inject Mounjaro?
Mounjaro is a once-weekly injection. You inject the same dose every 7 days on your chosen day. Each pre-filled KwikPen contains one week's dose. Set a reminder on your phone to maintain consistency, as regular timing helps your body adapt to the medication.
Which body areas can I inject Mounjaro into?
You can inject into your stomach (abdomen), upper thigh, or upper arm. Rotate your injection site each week — for example, use your stomach week 1, thigh week 2, arm week 3, then back to stomach. This reduces irritation and ensures even absorption over time.
How much does Mounjaro cost on the NHS?
Mounjaro is available on the NHS through specialist weight management services at no direct cost to eligible patients. However, access depends on your local ICB (Integrated Care Board) and specialist service availability. Waiting times vary by region from weeks to many months.
What is the starting dose of Mounjaro and how does it increase?
You start on 2.5 mg weekly for weeks 1–4. Your prescriber increases this by 2.5 mg every 4 weeks — to 5 mg, then 7.5 mg, 10 mg, 12.5 mg, and up to 15 mg maximum. Increases depend on your response and side effects; your prescriber guides the schedule.
Can I switch between NHS and private Mounjaro prescriptions?
Yes, you can move between routes, but inform both your previous and new prescriber about your current dose. Never overlap prescriptions. Your new prescriber will assess your ongoing suitability and confirm your dose. Switching should be managed carefully to maintain consistent weekly 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.