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 Fridge Correctly
Mounjaro (tirzepatide) is a prescription-only injection that requires careful storage to remain safe and effective. Proper fridge storage is essential for unopened KwikPen devices. This guide explains exactly how to store your Mounjaro at home in the UK, including the correct temperature, what to avoid, and how long you can keep it in the fridge. Understanding storage is just as important as understanding your dose titration schedule when starting this GLP-1 receptor agonist medication.
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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 — Refrigerator Requirements
Unopened Mounjaro KwikPen devices must be stored in a refrigerator at 2°C to 8°C. This is the standard fridge temperature range. Store your pens in the original carton to protect them from light exposure, which can damage the medication. The original packaging also helps prevent accidental freezing, which would render the medication unusable.
- Keep pens away from the freezer compartment — if frozen, do not use and consult your prescriber
- Do not store on the fridge door where temperature fluctuates when opened
- Place pens on a stable shelf toward the back of the fridge where temperature is most consistent
- Check the expiry date on the carton — unopened pens are usable until the printed expiry date if kept refrigerated
If your fridge temperature drops below 2°C or rises above 8°C consistently, the medication may be damaged. A fridge thermometer (available from any supermarket) can help you verify your fridge is at the correct temperature.
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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.
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After First Use — Room Temperature Storage
Once you have used your first injection from a KwikPen, you can store the pen at room temperature (below 30°C) for up to 30 days. This flexibility makes it easier to carry your pen with you or keep it accessible during your weekly injection day. However, if you prefer to keep it refrigerated after opening, this is also fine — just use it within 30 days of first use.
- Discard the pen 30 days after the first injection, even if medication remains
- Do not return an opened pen to the fridge then back to room temperature repeatedly
- Keep away from direct sunlight and heat sources
- Store out of reach of children and pets
Try our free GLP-1 weight loss calculator to help track your projected weight loss progress alongside your Mounjaro dose increases and storage timeline.
- 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 in the fridge?
Store unopened Mounjaro KwikPen devices at 2°C to 8°C in the refrigerator. This is the standard fridge temperature range in the UK. Keep the pen in its original carton to protect it from light and prevent accidental freezing. Do not store on the fridge door.
Can I freeze Mounjaro?
No. Do not freeze Mounjaro KwikPen devices. If a pen is accidentally frozen, do not use it. Freezing damages the medication and makes it unsafe to inject. If your fridge temperature drops below 2°C, adjust the thermostat or move your pens to a warmer area of the fridge.
How long can I keep Mounjaro in the fridge after opening?
Once you have injected from a KwikPen, you can store the remaining medication at room temperature (below 30°C) for up to 30 days. You must discard the pen after 30 days of first use, even if medication remains inside.
Can I keep Mounjaro in the fridge door?
No. Store unopened KwikPen devices on a stable shelf toward the back of the fridge, not on the door. The door experiences temperature fluctuations every time you open and close the fridge, which can damage the medication.
What if my fridge is too warm or too cold?
Check your fridge temperature with a thermometer — it should read 2°C to 8°C. If it's consistently outside this range, adjust the thermostat or contact the fridge manufacturer. For temperatures below 2°C, move your Mounjaro to a warmer shelf. Always consult your pharmacist if you suspect your medication has been stored incorrectly.
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