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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Where To Inject Mounjaro — Complete UK Guide
Mounjaro (tirzepatide) is a once-weekly injection that you can safely administer yourself at home using a pre-filled KwikPen device. The medication can be injected into three main areas of your body, and rotating your injection site each week helps prevent skin irritation and bruising. Understanding where to jab Mounjaro, how to access it in the UK, and what to expect from the injection process is essential for anyone considering this prescription weight management treatment. This guide covers injection technique, site rotation, and both NHS and private access routes in the UK.
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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 Sites — Where To Jab Safely
Mounjaro can be injected into three main body areas: the stomach (abdomen), the upper thigh, or the upper arm. Your stomach is the most common site and is easiest to self-inject. The upper thigh is the second most popular choice and equally straightforward to use alone. If injecting into your upper arm, you may need assistance from another person.
- Stomach: Inject at least 5cm away from your belly button. Pinch a fold of skin and inject at a 90-degree angle.
- Upper thigh: Inject on the front or outer area, at least 5cm away from the kneecap. You can pinch the skin or keep it flat.
- Upper arm: Inject into the back of the upper arm, midway between shoulder and elbow. This site usually requires help.
Rotate your injection site every week. This prevents lipodystrophy (changes to the skin and underlying tissue) and reduces bruising, pain, and irritation. Never inject into areas where the skin is tender, bruised, hard, or showing signs of scarring. Your prescriber or nurse can demonstrate the correct technique during your first consultation.
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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.
Accessing Mounjaro In The UK — NHS Vs Private Routes
NHS access: Mounjaro is available through NHS specialist weight management services (tier 3/4). You need a GP referral, and availability varies significantly by region and waiting lists can be lengthy. NICE has approved tirzepatide for NHS use, but access depends on your local Integrated Care Board (ICB). Private access: Mounjaro is available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. No NHS referral is needed. You'll complete a health questionnaire, speak with a prescriber, and receive a prescription if clinically appropriate. Private prescriptions typically cost £129–£320 per month depending on your dose and provider. Try our free GLP-1 weight loss calculator to estimate potential outcomes at different Mounjaro doses, and use our BMI calculator to check your baseline before starting treatment.
- 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.
What happens if I inject Mounjaro into the wrong place?
If you accidentally inject into an area with bruising or hardened tissue, you may experience increased discomfort or uneven medication absorption. Contact your prescriber for guidance. For routine injections, use only the approved sites (stomach, thigh, upper arm) and rotate weekly to prevent complications.
Can I switch Mounjaro injection sites within the same week?
Yes, you can inject into different approved sites if needed, but the standard guidance is to rotate sites weekly — injecting into a different body area each week rather than using the same site repeatedly.
How long does a Mounjaro KwikPen last?
Each pre-filled KwikPen contains four weekly doses. A single pen lasts approximately four weeks. Store unopened pens in the fridge at 2–8°C. After first use, you can keep the pen at room temperature (below 30°C) for up to 30 days.
Do I need a prescription to buy Mounjaro in the UK?
Yes, Mounjaro is prescription-only in the UK. You can obtain a prescription through NHS specialist weight management services or through a private online prescriber following a clinical assessment. Never buy Mounjaro without a valid UK prescription.
What should I do if I miss a Mounjaro injection?
If you remember within 4 days of your usual injection day, take the dose as soon as you can and continue your normal schedule. If more than 4 days have passed, skip that dose and inject on your normally scheduled day. Never take a double dose, and keep at least 3 days (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.