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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Should Mounjaro Be Kept In The Fridge?
Yes — unopened Mounjaro pens must be stored in a refrigerator between 2°C and 8°C. Once you start using a pen, you can keep it at room temperature (below 30°C) for up to 30 days before discarding. Understanding proper storage is essential to keep your tirzepatide injection safe and effective. This guide explains UK storage requirements, what happens if your Mounjaro gets too warm or freezes, and practical tips for managing your prescription at home or on the go.
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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 Refrigeration And Storage Requirements
Unopened Mounjaro pens must always be stored in a refrigerator at 2°C to 8°C — this is a cold chain requirement set by the manufacturer and the MHRA. Keep pens in their original carton to protect from light exposure. If your Mounjaro freezes (below 0°C), do not use it — frozen medication loses effectiveness and safety cannot be assured. Check the expiry date on the carton; unopened pens can be used until this date if continuously refrigerated.
After first use, your Mounjaro KwikPen can be stored at room temperature below 30°C for a maximum of 30 days. This means you can carry your pen in a bag during the day without needing a cool bag — making it practical for work or travel. After 30 days from first use, discard the pen safely (ask your pharmacist about needle disposal services in your area). Never store used pens back in the fridge once they have been brought to room temperature.
Keep your Mounjaro away from heat sources, direct sunlight, and extreme temperatures. Do not leave it in a hot car, on a sunny windowsill, or near radiators. If you travel by plane, carry your pen in your hand luggage (not checked baggage) to avoid freezing in cargo holds.
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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Travel Tips And Managing Your Mounjaro Prescription
If you're travelling within the UK or abroad, plan ahead. Bring your prescription documentation and pharmacy contact details. For journeys under a few hours, a small insulated cool bag with an ice pack (not in direct contact with the pen) keeps Mounjaro safe. Many pharmacies can issue replacement pens if yours is damaged during travel — speak to your prescriber or pharmacist before your trip.
At home, store your unopened pens on a dedicated shelf in the fridge — not in the door, where temperature fluctuates. Label them with your name and the date received. If you share a fridge with others, make this clear to avoid accidental use. Use our free BMI calculator to track your health progress while on Mounjaro, and consider our GLP-1 weight loss calculator to monitor projected outcomes alongside proper medication storage practices.
- 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 temperature should Mounjaro be stored at?
Unopened Mounjaro pens must be refrigerated at 2°C to 8°C in their original carton. Once opened, you can keep the pen at room temperature (below 30°C) for up to 30 days before discarding. Never freeze or expose to heat.
Can I store Mounjaro in the fridge door?
No — avoid the fridge door as temperatures fluctuate when the door opens and closes. Store unopened pens on a dedicated shelf in the coldest, most stable part of your fridge to maintain consistent temperature.
What happens if my Mounjaro freezes?
Do not use frozen Mounjaro. Freezing damages the medication and the MHRA cannot assures safety or effectiveness. If your pen freezes, contact your pharmacist or prescriber for a replacement.
How long can I keep Mounjaro at room temperature after opening?
Once you've used a Mounjaro KwikPen for the first time, it can stay at room temperature (below 30°C) for up to 30 days maximum. After 30 days, discard it safely even if there is medication remaining.
Can I put Mounjaro back in the fridge after taking it out?
No — once an opened pen has been at room temperature, do not return it to the fridge. Keep it at room temperature and use within 30 days. This prevents temperature shock which could affect the medication's stability.
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.