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 Room Temperature Storage — What You Need to Know
If you've been prescribed Mounjaro (tirzepatide) in the UK, understanding how to store your KwikPen correctly is essential for keeping the medication safe and effective. Once you've opened your first pen, you can store it at room temperature — but there are specific guidelines you need to follow. This guide explains NHS and MHRA-approved storage practices to ensure your treatment remains safe and maintains its potency throughout your weight management journey.
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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.
Room Temperature Storage Guidelines for Mounjaro
After opening your Mounjaro KwikPen, you can store it at room temperature below 30°C (86°F) for up to 30 days. This makes the injection convenient to carry or keep in a bedroom drawer without needing continuous refrigeration. However, once the 30-day window closes, you must discard the pen — even if it still contains medication. Do not attempt to refrigerate it again after keeping it at room temperature, as this may affect the medication's stability.
- Storage temperature: below 30°C (86°F)
- Maximum duration at room temperature: 30 days from first use
- Keep away from heat sources and direct sunlight
- Do not freeze the pen at any point
- Keep the pen in its original packaging if possible to protect from light
Before opening your first pen, Mounjaro KwikPens must be kept refrigerated at 2°C to 8°C (36°F to 46°F). This is why your pharmacy will deliver refrigerated pens, and you should store them in the fridge immediately upon receipt. Once you've used your first injection, you can transition to room temperature storage for the remaining three doses in that pen.
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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.
NHS and MHRA Guidance on Mounjaro Storage
The MHRA (Medicines and Healthcare products Regulatory Authority) — the UK's independent regulator for medications — has approved these storage guidelines as part of Mounjaro's product information. Your GP or prescriber should provide written storage instructions with your prescription, and your pharmacy will confirm the correct storage method when dispensing.
If you're unsure whether your pen has been stored correctly, or if it's been exposed to extreme temperatures, contact your pharmacy or GP before using it. Never use a pen that has been frozen, even if it has been thawed. Keep a note of the date you first opened each pen so you know when the 30-day window closes. Use our free BMI calculator to track your overall health progress alongside your Mounjaro treatment, and record any changes in weight or side effects in a progress journal to share with your prescriber at your next review.
- 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 an unopened Mounjaro KwikPen at room temperature?
No. Unopened pens must be stored in a refrigerator at 2°C to 8°C (36°F to 46°F) until you use them. Only after you've taken your first injection can you keep the remaining doses at room temperature for up to 30 days.
What happens if my Mounjaro is left at room temperature by accident before opening?
If an unopened pen has been left at room temperature for a few hours, it should still be safe — the medication has some tolerance to short-term temperature changes. However, if it's been left for more than 24 hours above 30°C or if you're unsure, contact your pharmacy. Do not use it if it has been frozen.
Can I put my opened Mounjaro pen back in the fridge if I've been carrying it at room temperature?
No. Once you've removed an opened pen from the refrigerator and stored it at room temperature, do not refrigerate it again. Repeated temperature changes can affect the medication's stability. Keep it at room temperature until the 30-day mark, then discard it.
How do I know if my Mounjaro has been damaged by temperature?
Check for visible signs: cloudiness or discolouration in the liquid (it should be clear), damage to the pen itself, or a broken safety cap. If the pen has been frozen, do not use it. When in doubt, contact your GP or pharmacy before injecting.
What should I do with my Mounjaro pen after 30 days at room temperature?
Dispose of it safely using the sharps disposal method advised by your pharmacy. Do not throw it in household waste or flush it down the toilet. Your pharmacy can advise on local sharps bins or home collection services — this is free on the NHS.
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.