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 In The Thigh Do You Inject Mounjaro
The upper thigh is one of three approved injection sites for Mounjaro (tirzepatide), alongside the stomach and upper arm. If you choose the thigh, you should inject into the outer area of the upper thigh — the front or outer-facing side — avoiding the inner thigh. This guide explains the exact positioning, rotation strategy, and safety tips for thigh injections in the UK, helping you use your Mounjaro KwikPen safely and effectively.
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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 Thigh Injection Site: Exact Positioning
The upper thigh is the safest area for Mounjaro injection. Specifically, inject into the outer aspect of the upper thigh — the front or side-facing area, not the inner thigh where blood vessels and nerves are closer to the surface. Aim for the area roughly 10 centimetres (4 inches) above the knee and 10 centimetres below the hip fold. This zone has adequate fatty tissue and minimal risk of hitting underlying structures. The upper thigh offers advantages over the stomach for some users: less visible bruising beneath clothing, easier self-administration without awkward arm positioning (unlike the upper arm), and a larger surface area for rotation. Your Mounjaro KwikPen is designed for easy thigh use — hold the pen perpendicular (at 90 degrees) to the skin and inject straight in. The needle is short and safe for thigh subcutaneous injection.
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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.
Injection Rotation: Why It Matters And How To Track It
Rotate your injection site each week to prevent lipodystrophy (lumpy or sunken areas of fat under the skin). If you inject into the thigh every week, vary the exact spot — left thigh one week, right thigh the next, or move within the upper thigh area. Never inject into the same spot twice in a row. Using your GLP-1 weight loss calculator can help you track your overall progress, and similarly, keeping a simple note of where you injected each week helps you stay organised. If you rotate between three injection sites (stomach, left thigh, right thigh), you can inject into each location every three weeks, allowing full recovery between injections to the same area. Rotation reduces pain, bruising, and skin complications — particularly important over the months-long course of tirzepatide 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.
Can I inject Mounjaro into the inner thigh?
No, avoid the inner thigh. Inject into the outer upper thigh only — the front or outer-facing side. The inner thigh has blood vessels and nerves closer to the surface, increasing risk of bruising and complications. Always use the outer thigh area, approximately 10cm above the knee and 10cm below the hip.
How deep should I push the Mounjaro needle into my thigh?
Hold your Mounjaro KwikPen perpendicular (at 90 degrees) to the skin and push the needle straight in until you hear or feel a click, then hold for 3 seconds. The needle length is designed for subcutaneous injection into thigh fat. You do not need to worry about depth — the pen is calibrated for safe administration.
What if I get bruising or lumps after Mounjaro thigh injections?
Minor bruising is normal and fades within days. Lumps or sunken areas suggest lipodystrophy, usually caused by repeated injections in the same spot. Rotate injection sites every week. If lumps persist, inform your GP or prescriber. Applying ice briefly before injection can reduce bruising risk.
Is the thigh safer than the stomach for Mounjaro injections?
Both are safe — it depends on your preference. The thigh offers easier self-injection positioning and less visible bruising. The stomach is also effective and easier for some users. Rotate between all three approved sites (stomach, left thigh, right thigh) to minimise complications and skin irritation.
How do I know if I've injected Mounjaro correctly into my thigh?
You should feel or hear a click from the KwikPen, see a small mark where the needle entered, and feel mild pressure. Hold for 3 seconds after the click. If you feel pain, severe resistance, or see significant bleeding, stop and contact your GP. Minor bleeding or discomfort is normal.
Ready to take control of your weight loss journey?
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