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
Mounjaro Storage Temperature — How to Store Your Pens Safely
Mounjaro (tirzepatide) KwikPen injections require careful temperature control to remain effective. Whether you've just received your prescription or are in the middle of your dose titration, correct storage is essential to ensure your medication works as intended. This guide explains the exact temperature requirements for both unopened and opened Mounjaro pens, plus practical UK storage advice to keep your injections safe and ready to use.
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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 Pens — Refrigerator Storage
Unopened Mounjaro pens must be stored in a refrigerator at 2°C to 8°C — this is the standard fridge temperature. Keep pens in their original carton to protect them from light damage. Do not freeze Mounjaro under any circumstances; if a pen accidentally freezes, discard it and do not use it, as freezing damages the medication and makes it unsafe.
- Store in the main fridge compartment, not the freezer or door shelves where temperature fluctuates
- Keep away from the back wall of the fridge where it may be coldest
- Store in the original protective carton until you're ready to use each pen
- Check the expiry date on your prescription before opening
- Unopened pens can be used until the expiry date printed on the carton if kept continuously refrigerated
If you travel or need to transport unopened pens, use an insulated cool bag with ice packs to maintain the correct temperature.
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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 First Use — Room Temperature Storage
Once you've used a Mounjaro pen for the first injection, you can store it at room temperature below 30°C for up to 30 days. This makes it convenient to keep your pen accessible for your weekly injections without needing constant refrigeration.
- Do not return a used pen to the fridge once you've started using it
- Keep away from heat, direct sunlight, and moisture
- Do not leave in hot cars or near radiators
- Discard the pen 30 days after first use, even if medication remains
- Mark the date you first used each pen on the carton to track the 30-day window
Track your usage dates in our free progress tracker to stay organised with your Mounjaro schedule and ensure you're using each pen safely within its storage 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 the fridge door?
No — the fridge door experiences temperature fluctuations from opening and closing. Store unopened pens in the main fridge compartment at 2–8°C. Temperature changes can reduce the effectiveness of tirzepatide, so consistent cold storage is essential.
What happens if Mounjaro freezes?
If your Mounjaro pen freezes, do not use it. Freezing damages the medication and makes it unsafe and ineffective. Discard the frozen pen and contact your prescriber or pharmacy for a replacement immediately.
Can I travel with Mounjaro?
Yes. For unopened pens, use an insulated cool bag with ice packs to maintain 2–8°C during travel. Once opened, used pens can travel at room temperature as long as they're kept below 30°C. Never leave Mounjaro in a hot car or direct sunlight.
How do I know when to discard a used pen?
Mark the first injection date on your pen's carton. Discard it exactly 30 days after first use, regardless of how much medication remains. This ensures you're always using fresh, effective medication as intended by your UK prescription.
What's the difference between Mounjaro and Wegovy storage?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) share the same storage rules: unopened at 2–8°C, and after first use at room temperature below 30°C for up to 30 days. Always follow the guidance on your specific prescription label.
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.