Left Your Mounjaro Out of the Fridge Overnight? Here's What to Know

Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are pre-filled, prescription-only injectable pens that are typically supplied and stored in the fridge. However, the product information for each medicine acknowledges that keeping a pen refrigerated at all times is not always practical — so both have an approved out-of-fridge window for use at room temperature.

What the guidance generally says

Check the leaflet in your pack or the official product entry on the electronic Medicines Compendium (medicines.org.uk) for the precise figures, because storage periods differ between products and can be updated. As a general principle, once a pen has been taken out of the fridge it should be kept below 30°C (86°F), away from direct sunlight and heat sources, and used within the window stated in your leaflet. After that window closes, the manufacturer advises disposing of the pen.

Does it matter whether the pen is opened or unopened?

The storage clock typically starts when the pen is first removed from the fridge, regardless of whether it has been used. An unopened pen that has been left out overnight is subject to the same time limit as one that has already been used for a first dose — so check the leaflet and note the date and time it came out. For more detail on the fridge rules that apply to your pen, see our pages on whether Mounjaro needs to stay in the fridge and how essential fridge storage really is.

Signs a pen may be compromised

If the solution looks discoloured, cloudy, or contains visible particles, do not use it — contact your prescriber or pharmacist. The same applies if the pen was left somewhere unusually warm (such as a car in direct sunlight) rather than simply at a cool room temperature.

You may also find it useful to read about whether you can return a Mounjaro pen to the fridge once it has been out — this is a related question the product information addresses specifically.

One of the most practical things you can do after an out-of-fridge incident is log exactly when the pen came out — so you always know how much of the permitted room-temperature window remains. GLP Trackr's dose logging feature lets you record the date, time, and dose strength of every injection, and you can add a note about storage to keep a clear record to discuss with your prescriber or pharmacist if needed.

Dose reminders in the app also mean your weekly injection is less likely to be forgotten, which is one of the most common reasons pens end up left out — a hurried morning where the pen was prepared and then not used. Setting a gentle reminder keeps your schedule on track and reduces the chance of a pen spending longer than intended at room temperature.

For a broader look at managing your Mounjaro journey week to week, visit the Mounjaro hub for guides on dosing, side effects, and tracking your progress.

Always follow the storage guidance of your prescriber, pharmacist, or the official product leaflet — if there is any doubt about whether a pen is still suitable to use, ask a healthcare professional before injecting.

Ready to keep a clear log of every dose and note? Download GLP Trackr on the App Store or Google Play and try it free for 7 days — no guesswork, just a clear record of your journey.