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 Storage Temperature — How to Keep Your Injection Safe
Mounjaro (tirzepatide) is a prescription-only weight management injection that requires careful storage to remain effective. Proper temperature control is essential — storing your KwikPen at the wrong temperature can damage the medication and reduce its effectiveness. This guide covers UK storage requirements for unopened and in-use Mounjaro pens, including how to transport them safely and what to do if your pen has been exposed to extreme temperatures. Understanding these storage requirements helps ensure your prescription medication remains safe and potent throughout your 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.
Unopened Mounjaro Storage Requirements
Unopened Mounjaro KwikPen devices must be stored in a refrigerator at 2°C to 8°C — this is the standard UK pharmaceutical storage temperature. Keep the pen in its original carton to protect it from light exposure, which can degrade the tirzepatide solution. Do not freeze your Mounjaro pen — if it has been accidentally frozen, do not use it and contact your pharmacist or GP for guidance. Unopened pens can be used safely until the expiry date printed on the carton, provided they have been stored continuously at the correct temperature. Before using an unopened pen, check that the medication inside is clear and colourless — if it appears cloudy, discoloured, or contains particles, do not use it and return it to your pharmacy. If you need to transport an unopened pen, use an insulated cool bag with ice packs to maintain the 2°C to 8°C temperature range during travel.
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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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In-Use and Room Temperature Storage
Once you have used your first dose from a Mounjaro KwikPen, you can store the pen at room temperature below 30°C for up to 30 days. This flexibility allows you to carry your pen with you without requiring constant refrigeration between weekly doses. After 30 days from first use, you must dispose of the pen safely — even if medication remains inside. Keep the in-use pen away from direct sunlight and heat sources such as radiators or car dashboards. If you accidentally leave an in-use pen in a warm environment (above 30°C) for more than a few hours, contact your pharmacist for advice before using it. Always keep your Mounjaro pen in a safe place away from children and pets. Use our free GLP-1 weight loss calculator to track your treatment progress alongside proper 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.
Can I store my unopened Mounjaro in the freezer?
No. Freezing damages tirzepatide and makes the pen unusable. Store unopened Mounjaro in a fridge at 2–8°C only. If your pen has been frozen, do not use it — contact your pharmacist or GP for a replacement.
How long can I use an in-use Mounjaro pen at room temperature?
You can store an in-use Mounjaro pen at room temperature (below 30°C) for up to 30 days from first use. After 30 days, dispose of the pen safely, even if medication remains.
What should I do if my Mounjaro pen has been left in a hot car?
If your pen has been exposed to temperatures above 30°C for more than a few hours, contact your pharmacist before using it. They can advise whether the medication is still safe to inject.
Do I need to keep my Mounjaro in the original carton?
For unopened pens, yes — store in the original carton to protect from light. For in-use pens, you can remove from the carton, but keep away from direct sunlight and heat.
Can I use my Mounjaro if it looks cloudy or discoloured?
No. Mounjaro should be clear and colourless. If it appears cloudy, discoloured, or contains particles, do not use it. Return it to your pharmacy and ask for a replacement.
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