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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How to Store and Refrigerate Mounjaro Correctly
Proper storage of your Mounjaro KwikPen is essential to maintain its effectiveness. Mounjaro (tirzepatide) is a prescription-only weight management injection that requires specific temperature control before and after first use. Understanding the correct refrigeration temperature, storage duration, and what to do if your pen is accidentally frozen will help you get the most from your treatment. This guide covers UK storage guidance and practical tips for keeping your Mounjaro safe at home.
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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.
Storage Requirements Before and After First Use
Unopened Mounjaro KwikPens must be stored in a refrigerator at 2°C to 8°C — this is the correct refrigeration temperature range. Keep the pen in its original carton to protect it from light. Unopened pens can be safely stored this way until the expiry date printed on the packaging.
After your first injection, the opened KwikPen can be kept at room temperature below 30°C for up to 30 days. Once you have used a pen for the first time, you no longer need to refrigerate it if you prefer room temperature storage — however, many people continue to refrigerate for convenience. After 30 days from first use, the pen must be disposed of safely, even if there is still medication remaining.
- Store in original carton away from direct sunlight and heat
- Do not freeze unopened or opened pens — if frozen, the medication is damaged and the pen cannot be used
- Check the expiry date before each injection
- Keep away from extreme temperatures and moisture
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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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Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Accessing Mounjaro in the UK — Cost and Prescription Routes
Mounjaro is available in the UK through two routes: NHS specialist services or private prescription. NHS access is through tier 3 specialist weight management services following GP referral, though availability varies significantly by region and waiting times can be lengthy. Private access is available through UK-licensed online prescribers following a clinical assessment, with costs typically ranging from £150–£250 per month depending on the dose — storage and refrigeration requirements are identical regardless of prescription route. Both routes require a prescription from a qualified healthcare professional, and your prescriber will discuss dose titration schedules and proper storage before your first injection.
- 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 is the correct temperature to refrigerate Mounjaro?
Store unopened Mounjaro KwikPens at 2°C to 8°C in a standard refrigerator. This is the only acceptable refrigeration range. After your first injection, the opened pen can be kept at room temperature below 30°C for up to 30 days. Never freeze your pen — if frozen, the medication is damaged and cannot be used safely.
Can I use Mounjaro that has been frozen?
No. If your Mounjaro KwikPen has been frozen, it must not be used. Freezing damages the tirzepatide medication and renders it unsafe. If your pen freezes accidentally, contact your prescriber or pharmacist for guidance on obtaining a replacement pen.
How long can I keep an opened Mounjaro pen at room temperature?
Once you have used your Mounjaro KwikPen for the first time, it can be stored at room temperature (below 30°C) for up to 30 days. After 30 days from first use, you must dispose of the pen safely, regardless of how much medication remains. Many people continue to refrigerate opened pens for convenience.
What should I do with Mounjaro if I'm travelling?
Keep unopened pens in a cool bag with ice packs to maintain 2–8°C if travelling for short periods. For longer journeys, portable insulin cooler bags designed for medicines are ideal. Once opened, your pen can be stored at room temperature for 30 days, making travel easier. Check your destination's temperature and plan accordingly.
Is NHS or private prescription Mounjaro different in terms of storage?
No. Storage and refrigeration requirements are identical regardless of whether your Mounjaro is prescribed through the NHS or privately. Both require the same temperature control before and after first use. Your prescriber will provide the same storage guidance with either prescription route.
Ready to take control of your weight loss journey?
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