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 to Inject Mounjaro — Safe Injection Sites
Mounjaro (tirzepatide) is injected once weekly under the skin, and you have flexibility in choosing your injection site. The main areas where you can safely inject Mounjaro are your stomach (abdomen), upper thigh, or upper arm — each offering practical advantages depending on your preference and comfort. Understanding the correct injection sites and rotation technique helps ensure consistent medication absorption and reduces the risk of skin irritation. This guide covers everything UK adults prescribed Mounjaro through NHS specialist services or privately need to know about safe injection site selection and best practice.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Approved Mounjaro Injection Sites and Rotation
Mounjaro can be injected into three main areas of the body:
- Stomach (abdomen): The most commonly used site. Inject into the soft tissue on your stomach, avoiding the area around your belly button (navel) by at least 5cm. This area is often easiest to access yourself.
- Upper thigh (front or outer side): A practical alternative if you prefer rotating away from your stomach. The outer thigh provides good soft tissue for injection and you can self-administer easily.
- Upper arm (back of the arm): Available if someone can help you inject, as this site is difficult to reach yourself. Ask a family member, partner, or healthcare professional to assist.
The KwikPen pre-filled injection device is designed for all three sites. Rotate your injection site each week — this means choosing a different location for each of your four weekly doses to prevent irritation, lipohypertrophy (thickened tissue), or lipoatrophy (thinned tissue) at any single site. Within each area, you can also rotate slightly — for example, injecting the right side of your stomach one week and the left side the next.
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.
Injection Technique and Safety Considerations
Before injecting, ensure your hands are clean and the injection site is clean and dry. Pinch the skin gently to create a firm area, then insert the needle at a 90-degree angle (perpendicular to your skin). The needle on the KwikPen is short and thin, designed for subcutaneous (under-skin) injection. Hold the pen against your skin for 10 seconds after the click sound to ensure the full dose is delivered — this is important for effective medication absorption. Avoid injecting directly into areas where you have bruising, hardness, thickening, dimpling, or discolouration. These signs may indicate lipohypertrophy and choosing fresh injection sites helps prevent complications. If you experience persistent injection site reactions — redness, swelling, or pain lasting more than a few days — contact your GP or prescriber. For NHS patients, your tier 3 specialist weight management service should provide injection training; for private patients, many online prescribing services include detailed guidance.
- 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 in the same spot every week?
No. Rotating injection sites weekly is important to prevent skin complications like lipohypertrophy (thickened tissue) or irritation. Use different areas of your stomach, thigh, and arm, and vary the exact spot within each area between injections.
Which injection site is easiest for self-injection?
The stomach (abdomen) is typically easiest because you can see and reach it yourself. However, the upper thigh is also accessible for self-injection. The upper arm is best if you have assistance, as it's difficult to reach yourself.
What should I do if I have redness or bruising at the injection site?
Minor bruising is common and usually resolves within a few days. Choose a different injection site for your next dose. If redness, swelling, or pain persists beyond a few days, contact your GP or prescriber to rule out infection or injection site reaction.
Do I need to warm the Mounjaro before injecting?
No. If your Mounjaro has been refrigerated, you can inject it cold, or leave it at room temperature for 15–30 minutes first for comfort. Never use heat sources like hot water — the medication should not be warmed artificially.
What angle should I use to inject Mounjaro?
Inject at a 90-degree angle (perpendicular) to your skin for subcutaneous injection. Pinch the skin gently, insert the needle straight in, and hold for 10 seconds after you hear the click to ensure full dose delivery.
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.