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
Mounjaro is a once-weekly injection that can be administered into your upper thigh, making it one of the most convenient injection sites for self-administration. If you've been prescribed tirzepatide through an NHS specialist weight management service or private prescriber, understanding the correct injection technique is essential for effective treatment. This guide covers the NHS-recommended approach to safe thigh injection and what to expect during your weight loss journey with this GLP-1 receptor agonist medication.
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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.
How To Inject Mounjaro Into Your Thigh — Safe Technique
The upper thigh is one of three approved injection sites for Mounjaro alongside the abdomen and upper arm. To inject correctly: wash your hands thoroughly, check the KwikPen for clarity (the liquid should be clear and colourless), and select a clean area on the outer upper thigh, roughly midway between hip and knee. Rotate your injection site each week — if you injected the right thigh last week, use the left thigh this week, or switch to your abdomen. Pinch the skin gently, insert the needle at a 90-degree angle, and hold the pen in place for 3 seconds while the dose is delivered. The needle will automatically retract after injection. Never massage the injection site afterwards — this can increase absorption speed. If you experience significant bruising, redness, or pain at injection sites, inform your prescriber or GP as this may indicate a technique adjustment is needed.
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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.
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Everything you need to understand your weight, explore medication options, and track your progress — completely free.
NHS Support And Aftercare For Mounjaro Injections
When you receive your Mounjaro prescription through an NHS tier 3 weight management service, specialist nurses will provide detailed injection training before your first dose. Your GP practice should be informed of your treatment so they can monitor your progress and blood sugar control if relevant. If you're prescribed through a private online consultation, the pharmacy will provide written instructions and video guidance — always watch these before self-injecting. Report any concerns about injection technique, unusual side effects, or complications to your GP or prescriber immediately. The combination of correct injection technique with a reduced-calorie diet and increased physical activity gives the best clinical outcomes, as demonstrated in NICE guidance and clinical trials. Track your progress and weight changes using our free progress tracker to monitor results over weeks and months.
- 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 anywhere on my thigh?
No — inject into the outer upper thigh, roughly between hip and knee. Avoid the inner thigh where there are more blood vessels and nerves. Always rotate sites weekly to prevent lipohypertrophy (thickening of fatty tissue) at injection sites.
What if I get bruising after injecting Mounjaro into my thigh?
Minor bruising is common and usually harmless. Apply a cold compress if needed. However, if bruising is severe, recurrent at the same site, or accompanied by swelling or warmth, contact your GP. This may indicate technique adjustment is needed.
How long does Mounjaro take to work if I inject into my thigh?
Absorption time is similar regardless of injection site (thigh, abdomen, or arm) — usually 24–72 hours. Clinical effects on appetite typically develop within 3–5 days. Full benefit may take several weeks as your dose is gradually increased.
Do I have to inject Mounjaro into my thigh, or can I use my stomach instead?
You have three approved sites: upper thigh, abdomen, or upper arm (with assistance). Rotate between sites weekly to prevent skin complications. Many people alternate between thigh and abdomen for convenience.
What should I do if I accidentally hit a blood vessel during thigh injection?
Minor bleeding is not serious. Apply gentle pressure with a cotton ball for a few seconds. If bleeding is heavy, won't stop, or is accompanied by sudden pain or swelling, contact your GP or call 111 for advice.
Ready to take control of your weight loss journey?
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