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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Mounjaro Injection Sites: Using Your Arm
If you're prescribed Mounjaro in the UK, you may choose to inject into your upper arm as one of three approved injection sites. This guide covers where exactly to inject, how to access this weekly weight loss injection in the UK, and what you can expect to pay privately or through the NHS. We'll explain the difference between NHS and private routes, and what the online consultation process involves.
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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 Injection Sites and How to Use Your Arm
Mounjaro is injected once weekly using a pre-filled KwikPen device, and you have three approved injection site options: your stomach (abdomen), upper thigh, or upper arm. If you choose your arm, you'll inject into the outer upper arm area, roughly midway between your shoulder and elbow. The upper arm is a convenient site because it's easy to access, though most users find the stomach easiest for self-injection without assistance.
- Rotate your injection site each week to reduce skin irritation
- Never inject into the same spot twice in a row
- Your prescriber or pharmacist will show you the correct injection technique
- The injection takes just a few seconds
- Use a fresh needle for each dose
If you're using your arm, you may need assistance to reach comfortably, or you can use a mirror. Always check the KwikPen for any visible particles before injecting—if the solution looks cloudy or discoloured, do not use it.
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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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Mounjaro Cost and Access in the UK: NHS vs Private
In the UK, Mounjaro is available through two routes: NHS specialist weight management services or private prescription from a licensed online pharmacy. NHS access is through tier 3 specialist services (usually requiring GP referral), but availability varies widely by region and waiting lists can be months to years. Privately, Mounjaro costs approximately £130–£320 per month depending on your dose, with most users starting at 2.5 mg and titrating up weekly.
- Private prescriptions require an online clinical assessment with a UK-licensed prescriber
- Assessment typically costs £20–£50 and takes 10–15 minutes
- Once approved, your prescription is sent to a GPhC-registered pharmacy
- Delivery usually arrives within 24–48 hours
- Private costs are not refundable if you decide to stop
- 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 arm myself?
Yes, you can self-inject into your upper arm, though many people find the stomach easier. Your prescriber or pharmacist will demonstrate the correct technique. If you prefer arm injections, consider using a mirror or asking a family member to help you position the KwikPen correctly.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs range from approximately £130–£320 per month depending on your dose. Starting doses (2.5 mg) are typically cheaper than maximum doses (15 mg). Some private providers offer discounts for purchasing multiple months upfront. Always check the total cost including the clinical assessment fee before committing.
How do I get Mounjaro on the NHS in the UK?
You'll need a referral from your GP to a tier 3 specialist weight management service. However, NHS availability varies significantly by region and waiting lists can be very long. Your GP can advise whether your local integrated care board (ICB) currently offers Mounjaro through NHS services and what the waiting time is.
What's involved in a private online consultation for Mounjaro?
You'll complete a health questionnaire and have a brief video or phone call with a UK-licensed prescriber (usually 10–15 minutes). They'll assess your BMI, medical history, current medications, and suitability for Mounjaro. If approved, they'll issue a prescription to a GPhC-registered pharmacy, which dispenses and delivers your medication.
Is Mounjaro the same as a weekly weight loss injection?
Yes, Mounjaro is a once-weekly weight loss injection containing tirzepatide, a GIP and GLP-1 receptor agonist. It's different from daily injections like Saxenda (liraglutide). In clinical trials, Mounjaro showed average weight loss of 15–21% of body weight, though individual results vary significantly alongside diet and exercise changes.
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.