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
Mounjaro Injection Sites — Where and How to Inject Safely
Mounjaro is a once-weekly weight loss injection licensed in the UK for adults with a BMI of 30 or above, or 27 and above with weight-related health conditions. Understanding where and how to inject Mounjaro safely is essential if you're prescribed this medication. This guide covers approved injection sites, rotation techniques, storage requirements, and how to access Mounjaro in the UK through both NHS specialist services and private prescription routes.
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.
Approved Mounjaro Injection Sites and Rotation Technique
Mounjaro comes as a pre-filled KwikPen device designed for self-injection once weekly. The approved injection sites are: stomach (abdomen) — the most commonly used site; upper thigh — easy to access; and upper arm — requires assistance from another person. To minimise bruising and injection-site reactions, it's essential to rotate your injection site each week. For example, use your abdomen one week, your thigh the next week, and your arm the following week, then repeat the cycle. Avoid injecting into the same spot within 2–3 cm of your previous injection. If you experience redness, swelling, or pain at the injection site that persists beyond a few days, inform your GP or prescriber. This weekly weight loss injection method is straightforward once you've been shown the correct technique by your healthcare professional or pharmacist.
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.
Accessing Mounjaro in the UK — NHS and Private Routes
In the UK, Mounjaro can be accessed through two main routes. NHS access is through tier 3 or tier 4 specialist weight management services — you'll need a referral from your GP, though availability and waiting times vary significantly by region. Private access is through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber — no GP referral is required. Once a prescription is issued, your pharmacist will dispense your Mounjaro pens and provide injection training. Before starting, you'll be assessed for eligibility based on your BMI, health conditions, and current medications. Calculate your BMI using our free BMI calculator to see whether you may meet the eligibility criteria.
- 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.
What are the four approved injection sites for Mounjaro?
The approved sites are your stomach (abdomen), upper thigh, upper arm, and the back of your arm. Most people use their abdomen or thigh as these are easiest to access. Rotating between sites weekly helps prevent injection reactions and bruising.
How do I store my Mounjaro KwikPen after opening?
Once you've opened your first pen, store it at room temperature (below 30°C) for up to 30 days. Unopened pens must stay in the refrigerator at 2–8°C. Never freeze your pen — if it freezes, discard it. Keep pens away from heat and direct sunlight.
Can I switch between different injection sites during my treatment?
Yes, rotating between approved sites each week is recommended to reduce injection-site reactions and bruising. Avoid injecting into the same spot within 2–3 cm of your previous injection site. Your pharmacist or healthcare professional will show you how to rotate safely.
How long does it take to see results with Mounjaro injections?
Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly. Weight loss is typically gradual and depends on dose, adherence, diet, and physical activity. Your prescriber will monitor your progress regularly.
What's the difference between accessing Mounjaro via NHS or private prescription in the UK?
NHS access requires a GP referral to specialist services and may have waiting lists, but is free once approved. Private access involves an online consultation with a UK-licensed prescriber and costs approximately £129–£320 per month depending on dose. Both routes require clinical assessment — you cannot access Mounjaro without a prescription.
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.