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 Into Your Thigh
If you've been prescribed Mounjaro (tirzepatide), learning the correct injection technique is essential for safe and effective treatment. The thigh is one of three approved injection sites, and many people find it convenient for self-administration. This guide walks you through the proper location, technique, and safety considerations for injecting Mounjaro into your thigh, helping you build confidence with your once-weekly prescription injection.
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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 Sites and Technique
Mounjaro is delivered via a pre-filled KwikPen device, which you inject once weekly into one of three approved sites: the stomach (abdomen), upper thigh, or upper arm. The thigh is an excellent choice for self-injection because it's easy to access and you can see the injection site clearly.
- Location: Use the outer front area of your thigh, roughly between your hip and knee. This is the safest and most accessible area for self-injection.
- Rotation: Rotate your injection site each week — if you injected your left thigh last week, use your right thigh this week, or choose a different area on the same thigh at least 2cm away from your previous injection.
- Skin pinch: Gently pinch the skin on your thigh to create a fold. Some people prefer to inject without pinching, depending on how much fat is present in the area.
- Angle: Insert the needle at a 90-degree angle (straight in) to the skin. This ensures the medication reaches the subcutaneous tissue correctly.
Always follow the specific instructions included with your KwikPen, as injection technique is critical for medication effectiveness and dose titration through the treatment schedule.
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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.
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Safety, Storage, and When to Seek Help
Before each injection, check that your Mounjaro KwikPen is stored correctly — unopened pens should be refrigerated at 2–8°C, but once you start using a pen, you can store it at room temperature (below 30°C) for up to 30 days. Inspect the liquid in the pen; it should be clear and colourless. Do not use the pen if the solution is cloudy or discoloured.
Common side effects after injection include mild redness, bruising, or pain at the injection site — these usually resolve within a few hours. However, if you experience severe pain, significant swelling, signs of infection, or an allergic reaction, contact your GP or call 111 immediately. Never reuse needles, and always dispose of used pens safely in a sharps bin.
- 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 into my thigh if I have very little fat there?
Yes. If you have minimal fat on your thigh, you can still inject Mounjaro safely by gently pinching the skin to create a small fold before inserting the needle. Alternatively, you may find the stomach or upper arm more comfortable. Discuss any concerns with your prescriber or nurse.
How far apart should injection sites be on the same thigh?
Space injection sites at least 2cm (roughly the width of a finger) apart. Rotating sites helps prevent skin irritation, lipodystrophy (changes in fat distribution), and injection site reactions. Many people find it helpful to mark their thigh mentally or use a simple chart to track where they've injected.
Is it normal to feel a bruise after a Mounjaro thigh injection?
Mild bruising after a Mounjaro injection is common and usually harmless. It typically fades within a few days. However, if bruising is severe, persistent, or accompanied by significant pain or swelling, contact your GP to rule out an infection or other complication.
Do I need to use an ice pack before injecting Mounjaro into my thigh?
You don't need to, though some people find it helpful. A brief ice pack application (30 seconds) can numb the area slightly and reduce discomfort. However, make sure the skin is warm and dry before injection, as cold skin can make the needle insertion more difficult.
What's the difference between injecting Mounjaro and Wegovy into the thigh?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) use similar injection techniques and thigh injection is approved for both. The main difference is their mechanism: Mounjaro is a dual GIP and GLP-1 agonist, whilst Wegovy is a GLP-1 agonist only. Your prescriber will advise which is suitable for you based on your clinical assessment and eligibility.
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