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
How To Prepare Your Mounjaro Pen
Preparing your Mounjaro KwikPen correctly before each injection is essential for safety and effectiveness. This guide walks you through the exact steps recommended in the UK, from storage checks to injection readiness. Proper preparation ensures you're using your tirzepatide prescription safely and helps you get the most from your weight management treatment.
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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.
Step-By-Step Preparation Instructions
Remove from the fridge: Take your Mounjaro KwikPen out of the refrigerator 15–30 minutes before your scheduled injection. The pen should warm to room temperature — this reduces injection discomfort and helps the medication flow smoothly.
Check for damage: Inspect the pen for cracks, leaks, or cloudiness. If the liquid appears cloudy, discoloured, or contains particles (it should be clear and colourless), do not use it. Contact your pharmacist immediately.
Confirm the dose: Check the label to verify you are using the correct dose for your week. Your prescriber will have indicated which dose you should be on.
Prepare the injection site: Choose your injection site (abdomen, thigh, or upper arm). Clean the skin with an alcohol wipe and let it dry completely — injecting into wet skin increases the risk of infection.
Remove the needle cap: Twist the needle cap off the pen immediately before injection. Do not remove it earlier — the cap protects the needle.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
After Injection And Storage
After injecting, place the used needle in a sharps bin — never dispose of needles in household waste. If you don't have a sharps bin, ask your pharmacist for one or contact your local GP surgery for disposal advice.
Storage between injections: Store your Mounjaro pens in the refrigerator at 2–8°C in the original carton (protects from light). Once you've started using a pen, you can keep it at room temperature below 30°C for up to 30 days. If your pen has been left above 30°C or frozen, do not use it — discard safely at a pharmacy. Always keep your current pen away from direct heat and sunlight.
If you're unsure about any step, your pharmacist or GP can demonstrate the correct technique for you.
- 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 use my Mounjaro pen straight from the fridge?
It's possible but not recommended. Letting the KwikPen warm to room temperature for 15–30 minutes makes the injection more comfortable and the medication flows better. Cold injections can be more painful and may delay absorption slightly.
What should I do if my Mounjaro pen looks cloudy or discoloured?
Do not use it. Mounjaro solution should be clear and colourless. If it appears cloudy, discoloured, or has particles, contact your pharmacist immediately. Using damaged medication could be ineffective or unsafe.
How do I know which dose to inject each week?
Check the label on your KwikPen — it clearly states the dose (2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, or 15 mg). Your prescriber will have told you which dose week you're on. Keep a calendar or set a phone reminder to track your dose progression.
Can I reuse needles on my Mounjaro pen?
No. Each needle should be used once only. Always use a new needle for each injection. Reusing needles increases infection risk, blunts the needle point, and can damage the pen mechanism. Each KwikPen comes with guidance on needle attachment.
What's the safest way to dispose of my used needles?
Place needles in a sharps bin (a hard plastic container designed for this purpose). Ask your pharmacist for a sharps bin if you don't have one. Some NHS GP surgeries and pharmacies will also dispose of sharps for you free of charge.
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.