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 Inject Mounjaro Into Your Thigh
Injecting Mounjaro (tirzepatide) into your thigh is one of three approved injection sites and one of the most convenient options for self-administration. Your GP or prescriber will provide training on the correct injection technique, but understanding the practical steps beforehand can help you feel more confident. This guide covers thigh injection for Mounjaro in a UK context, including what to expect and how to do it safely.
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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 Thigh Injection — Step-by-Step Technique
Preparing your thigh for injection:
- Choose the upper outer area of your thigh — between your hip and knee, on the outer side
- Rotate injection sites with each weekly dose — if you injected the left thigh last week, use the right thigh this week, then your stomach next week
- Inspect the KwikPen before use; the liquid should be clear and colourless
- Let the pen warm to room temperature for at least 15 minutes if stored in the refrigerator
During injection: Clean the skin with an alcohol wipe and let it dry. Pinch the skin lightly, insert the needle at a 90-degree angle, press the injection button until you hear a click, hold for 3 seconds, then slowly withdraw. Do not rub the injection site. The entire process takes less than one minute.
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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.
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NHS Eligibility and Mounjaro Access in the UK
Mounjaro is available in the UK through NHS specialist weight management services and through private online prescribing with UK-licensed prescribers. NHS access is typically via referral to a tier 3 specialist weight management service, though availability varies significantly by region and waiting times can be lengthy. Private access is available through GPhC-registered online pharmacies following a clinical assessment. Your prescriber will provide full injection training as part of your prescription, including technique, site rotation, and needle disposal. Always ask your prescriber or pharmacist to demonstrate the injection technique before you self-inject for the first time — this is standard practice and removes any uncertainty.
- 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 inject Mounjaro anywhere on my thigh?
No. Inject into the outer upper area of your thigh, roughly between your hip and knee. Avoid areas close to bones, scars, or bruises. Rotate between your left thigh, right thigh, stomach, and upper arm across different weeks to reduce irritation and lipohypertrophy (thickened skin).
Does Mounjaro injection hurt when injected into the thigh?
Most people report minimal pain — the needle is very fine (29 gauge). You may feel a small pinch or pressure. If you experience sharp pain, stop and check your technique. Pain typically indicates incorrect angle or needle placement. Your prescriber can show you the correct technique during your initial training.
How often should I rotate my thigh injection site?
Rotate your injection site with each weekly dose. Use a different site each week across all approved areas: left thigh, right thigh, stomach, and upper arm. This reduces the risk of lipohypertrophy and ensures consistent absorption. Create a simple rotation schedule to keep track.
What should I do if I accidentally inject Mounjaro into a bruise or scar?
If you have an obvious bruise or scar, choose a different injection site. If you've already injected into a minor bruise, this is usually not dangerous, but continue rotating sites as normal. Avoid injecting into areas with active inflammation, redness, or tenderness.
Is thigh injection better than stomach or arm injection for Mounjaro?
All three approved sites — thigh, stomach, and upper arm — are equally safe and effective. The thigh is convenient for self-injection and many people find it more comfortable than the stomach. Choose based on your preference and comfort, and rotate between sites weekly as recommended.
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