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
Where Do I Inject Mounjaro โ Safe Injection Sites
If you've been prescribed Mounjaro (tirzepatide) in the UK, knowing where and how to inject it safely is essential. Mounjaro comes as a pre-filled KwikPen device and is injected once weekly under the skin. This guide explains the approved injection sites, rotation guidance, and practical tips for safe administration alongside NHS prescribing context.
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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/mยฒ).
While BMI isn't a perfect measure โ it doesn't account for muscle mass, bone density, or fat distribution โ 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 โ 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.
Approved Mounjaro Injection Sites
Mounjaro can be injected into three main areas of the body:
- Stomach (abdomen) โ the most common injection site. Inject at least 5cm away from your belly button and avoid scar tissue or bruised areas.
- Upper thigh (front and outer area) โ an easily accessible alternative site, suitable for self-injection.
- Upper arm (back of the upper arm) โ best when someone else administers the injection, as it's more difficult to reach yourself.
You should rotate your injection site each week to reduce the risk of skin problems, lipohypertrophy (thickened skin), and injection site reactions. This means if you inject into your stomach one week, choose your thigh the following week, then your arm, then return to the stomach. Always allow at least 3cm between injection points within the same area. Mounjaro is injected subcutaneously (under the skin), not into muscle or vein.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care โ 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 โ 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 โ completely free.
NHS Prescribing Context & Injection Support
If you're receiving Mounjaro through an NHS specialist tier 3 weight management service, your prescriber or nurse will demonstrate the correct injection technique before you start. They'll show you how to hold the KwikPen, select your injection site, pinch the skin, and administer the dose. Most adults can self-inject after this training. Your GP practice or the specialist clinic can also answer questions about injection technique at any time. If you find self-injection difficult, some NHS services may offer nurse-administered injections, though this varies by region. Always check your patient information leaflet (PIL) and follow your prescriber's guidance, as injection instructions are critical to safe and effective use.
- 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 โ 5mg โ 7.5mg โ 10mg โ 12.5mg โ 15mg
- GLP-1 receptor agonist
- Up to 15โ17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg โ 0.5mg โ 1mg โ 1.7mg โ 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 | 15โ22.5% | 12โ17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20โ32 weeks | 16โ20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | ยฃ150โยฃ250/month | ยฃ150โยฃ300/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 โ 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 into the same spot every week?
No. You should rotate injection sites each week to prevent skin problems and lipohypertrophy (thickened or hardened skin). Rotate between your stomach, thigh, and upper arm, and allow at least 3cm between injection points within the same area. Proper rotation helps ensure consistent absorption and reduces injection site reactions.
What angle should I inject Mounjaro at?
Inject at a 90-degree angle (straight in) when pinching the skin, or at a 45-degree angle if you have very little skin to pinch. Your prescriber or nurse will demonstrate the correct angle during your training. The KwikPen is designed for subcutaneous injection, and the needle length is calibrated for this depth.
Can someone else inject my Mounjaro for me?
Yes. If you're uncomfortable self-injecting, a family member or carer can administer the injection after proper training. The upper arm is often the easiest site for someone else to inject. Always ensure whoever administers it has been shown the correct technique by a healthcare professional.
What should I do if I hit a blood vessel or feel pain during injection?
If you see blood or feel sharp pain, remove the pen and apply gentle pressure with a cotton ball. Don't use that injection site again. Contact your GP or prescriber if you experience severe pain, significant bleeding, or signs of infection (redness, warmth, swelling). Most minor bleeds are harmless, but your healthcare team can advise.
Does the KwikPen need to be at room temperature before injection?
Yes. Remove the KwikPen from the fridge 30 minutes before injection to allow it to reach room temperature. Injecting cold Mounjaro can be uncomfortable. Allow it to sit on a clean surface โ never use external heat sources. Once it has been used, it can be kept at room temperature (below 30ยฐC) for up to 30 days.
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.