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 Mounjaro in the UK
Storing Mounjaro (tirzepatide) correctly is essential to maintain its effectiveness and safety. This prescription-only weight loss injection requires specific storage conditions depending on whether your KwikPen is unopened or in use. Proper storage protects the medication and ensures it works as intended when you're ready to inject. This guide covers UK-specific storage requirements, temperature guidance, and what to do if storage goes wrong.
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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 for Unopened Mounjaro Pens
Unopened Mounjaro KwikPens must be stored in a refrigerator at 2°C to 8°C. This temperature range is critical — too warm and the medication degrades; too cold and freezing damage can occur. Keep your pens in the original carton to protect them from light exposure, which can also affect the medication's stability. Check the expiry date on your pen before use — if kept in the correct temperature, you can use Mounjaro until the expiry date printed on the carton.
Never freeze Mounjaro. If a pen has been frozen, do not use it — contact your prescriber or pharmacist for guidance on replacement. Freezing damages the medication's molecular structure and makes it unsafe and ineffective. Store unopened pens in the main body of your refrigerator, not in the freezer compartment or door, as these areas experience temperature fluctuations.
- Keep in original carton for light protection
- Maintain 2–8°C at all times
- Check expiry date before use
- Never store in freezer or door compartments
Clinically BackedWeight Loss
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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.
Storage After First Use (In-Use Pens)
Once you've used a Mounjaro KwikPen for the first time, storage requirements change. In-use pens can be stored at room temperature (below 30°C) for up to 30 days. This means you don't need to refrigerate the pen you're actively using each week, making it more convenient to carry or keep at home. However, you must still keep it away from direct heat and sunlight — a cool, dry cupboard or drawer is ideal.
After 30 days from first use, discard the pen even if it contains remaining doses. Mark the date you first use each pen so you can track when the 30-day window closes. If you won't be using a pen for longer than 30 days, keep it refrigerated instead. Individual pens contain four weekly doses, so most users will use an entire pen within the 30-day window.
- 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 store Mounjaro in my kitchen cupboard?
No — unopened pens must be refrigerated at 2–8°C. Once you start using a pen, you can store it below 30°C for up to 30 days, but keep it away from direct heat, sunlight, and humidity. A cool, dry cupboard is acceptable for in-use pens, but the refrigerator is safer for unopened pens.
What happens if Mounjaro freezes?
Do not use a frozen Mounjaro pen. Freezing damages the medication's structure, making it ineffective and potentially unsafe. If your pen freezes, contact your prescriber or pharmacist immediately. They can advise whether your pen can be replaced or if you need guidance on your next dose.
How long does an unopened Mounjaro pen last in the fridge?
Unopened pens can be stored until the expiry date printed on the carton, provided they remain refrigerated at 2–8°C in the original carton. Check the expiry date when you receive your pens and before each use.
Can I travel with Mounjaro on an aeroplane?
Yes, you can travel with Mounjaro. Unopened pens should remain in a cool bag with ice packs to maintain 2–8°C during travel. Once in use, pens can stay at room temperature for 30 days, making them portable. Check airline rules about transporting prescription medication — you'll need your prescription label and prescriber's letter.
How do I know when to replace an in-use pen?
Mark the first-use date on your in-use pen. Discard it after 30 days, even if doses remain. Each KwikPen contains four weekly doses, so most users complete one pen within 30 days. Always use a new pen after the 30-day window closes.
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.