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
Can You Inject Mounjaro in Your Thigh?
Yes, you can inject Mounjaro in your thigh — it's one of three approved injection sites in the UK. The upper thigh is a safe and convenient location for your once-weekly tirzepatide injection, though you'll need to rotate sites each week to prevent irritation. This guide explains safe injection technique, how Mounjaro compares to Wegovy, and what to expect from your KwikPen device.
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.
Mounjaro Injection Sites and Technique
Mounjaro approved injection sites in the UK are:
- Upper thigh (front or outer side)
- Stomach (abdomen) — most commonly used
- Upper arm — requires assistance
The upper thigh is a popular choice because it's easy to access without help. Rotate your injection site each week — never inject in the same spot twice in a row, as this increases bruising and skin irritation risk. If injecting in your thigh, alternate between your left and right leg weekly, and vary the exact spot on the thigh to distribute injections across the area.
Your KwikPen device comes with a fine 32-gauge needle pre-filled with your tirzepatide dose. Inject at a 90-degree angle (straight in) into the fatty tissue, not into muscle. Hold the pen in place for 3 seconds after injection to ensure full delivery. Do not massage the injection site afterwards.
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.
Mounjaro vs Wegovy: Key Differences
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only once-weekly injections licensed in the UK for weight management. The main difference is their mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy activates GLP-1 only. In clinical trials, Mounjaro showed average weight loss of 15–21% body weight, compared to Wegovy's approximately 15% — though individual results vary significantly.
Both medications can be injected in the thigh using the same technique. Eligibility is assessed on an individual basis by your prescriber. Your GP or licensed prescriber will determine which medication, if any, is appropriate for you following a clinical assessment of your health, weight, and medical history.
Both medications can be injected in the thigh using the same technique. Eligibility is assessed on an individual basis by your prescriber. Your GP or licensed prescriber will determine which medication, if any, is appropriate for you following a clinical assessment of your health, weight, and medical history.
- 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.
Is the thigh the best place to inject Mounjaro?
The thigh is one of three approved sites and is popular because it's convenient and doesn't require assistance. The stomach is the most commonly used site. Choose the site based on comfort and accessibility. What matters most is rotating sites weekly to prevent irritation and bruising.
Can you use Mounjaro KwikPen on your own thigh?
Yes, you can inject your thigh alone using the KwikPen. The pre-filled pen is designed for self-injection. The upper arm requires help from another person, but the thigh and stomach are accessible for self-administration.
How deep should you inject Mounjaro in the thigh?
Inject Mounjaro into the fatty tissue layer (subcutaneous injection), not into muscle. Use a 90-degree angle and inject straight in. Your KwikPen needle is 32-gauge and short enough for safe subcutaneous injection when used correctly. Your prescriber will provide injection training.
What's the difference between Mounjaro and Wegovy injection sites?
Both Mounjaro and Wegovy use the same three approved injection sites: thigh, stomach, and upper arm. The injection technique is identical. The main differences are their mechanisms (dual GIP+GLP-1 vs GLP-1 only) and average weight loss outcomes in clinical trials, which vary individually.
Can you inject Mounjaro in the same thigh twice?
No — rotate injection sites weekly to prevent bruising and skin irritation. If injecting in your thigh, alternate between left and right legs, and vary the spot on each thigh. Never use the exact same injection site within 7 days. Site rotation is essential for safe, comfortable ongoing treatment.
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.