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 In Your Thigh
The thigh is one of the three recommended injection sites for Mounjaro (tirzepatide), a prescription-only once-weekly weight management injection licensed in the UK. Proper injection technique is important for safety and medication effectiveness. This guide explains exactly where and how to inject Mounjaro into your thigh, plus how thigh injections compare to other injection sites and to Wegovy alternatives. Always follow your prescriber's instructions and the guidance in your Mounjaro KwikPen patient information leaflet.
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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
The upper outer thigh is the recommended injection site for Mounjaro when self-injecting. Choose the outer top area of your thigh, roughly halfway between your hip and knee, on the front or side of the thigh — avoid the inner thigh and the area directly above the kneecap. Your prescriber or nurse should demonstrate the technique before your first injection at home.
- Pinch a fold of skin and fat between thumb and fingers
- Insert the needle at a 90-degree angle (straight in, not at an angle)
- Release the skin fold once the needle is inserted
- Hold the KwikPen in place for 3 seconds after injection starts
- Remove the pen and apply gentle pressure with a tissue if needed
Rotate your injection site each week — if you injected your left thigh last week, use your right thigh this week, or alternate to your stomach or upper arm. Rotating sites helps prevent lipohypertrophy (thickened skin) and reduces injection-site reactions. Do not inject into areas with bruising, redness, or tenderness from a previous injection.
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Mounjaro vs Wegovy: Injection Sites and Mechanism
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) use the same three injection sites: thigh, stomach, and upper arm. The key difference is their mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 agonist only. In clinical trials, Mounjaro showed greater average weight loss (approximately 20.9% at the maximum 15mg dose) compared to Wegovy (approximately 14.9% at 2.4mg), though individual results vary significantly. Both require a UK prescription and clinical assessment to determine suitability. Your GP or prescriber will discuss which medication, if either, is appropriate for your specific health circumstances.
- 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 every week?
Yes. You can use your thigh as your injection site every week by rotating between left and right thigh. However, the NHS and your prescriber recommend rotating between all three sites (stomach, thighs, upper arm) each week to prevent skin thickening and reduce injection reactions. This gives your skin time to recover between injections in the same area.
What's the difference between injecting Mounjaro in the thigh versus stomach?
The thigh, stomach, and upper arm all work equally well for Mounjaro absorption and effectiveness. The thigh is convenient for self-injection and many people find it comfortable. The stomach is often quickest to access. Choose whichever site feels most comfortable for you and rotate weekly. Your prescriber will advise if any site is unsuitable.
Does Mounjaro work better if injected in a specific site?
No. Clinical evidence shows that Mounjaro (tirzepatide) works equally well regardless of injection site — thigh, stomach, or upper arm all achieve the same medication absorption and effect. Site choice is about your comfort and ease of access. What matters is proper injection technique and rotating sites to avoid skin complications.
How does Mounjaro's injection site compare to Wegovy?
Mounjaro and Wegovy use identical injection sites: upper thigh, stomach, and upper arm. Both are once-weekly injections requiring the same rotation approach. The difference between them is chemical (dual GIP+GLP-1 versus GLP-1 only) and dose range, not injection location. Your prescriber will discuss which medication suits your health needs.
What should I do if I develop a lump or redness at my Mounjaro thigh injection site?
Mild redness, bruising, or swelling at the injection site is common and usually settles within a few hours or days. If you develop a persistent lump, severe pain, warmth, or increasing redness lasting more than a few days, contact your GP or the prescriber who issued your Mounjaro prescription. Do not inject into that site again until it has fully healed. Rotating sites helps prevent this.
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