What Happens If Mounjaro Is Not Refrigerated?

Mounjaro (tirzepatide) is a biological medicine supplied as a pre-filled pen. Like most injectable biologics, it is sensitive to extremes of temperature in both directions.

If Mounjaro gets warm or is left out of the fridge

Biological medicines can lose potency when exposed to temperatures above the recommended storage range for longer than the permitted period. If a pen has been left out beyond the timeframe stated in the leaflet, the active substance (tirzepatide) may have begun to break down. A degraded pen can look identical to an intact one — the liquid may appear unchanged — so appearance alone is not a reliable check. Check the specific out-of-fridge storage window in your leaflet or on the electronic Medicines Compendium (eMC); if that window has been exceeded, contact your prescriber or pharmacist before using the pen.

If Mounjaro freezes

Freezing is also a problem. Biological medicines should never be frozen; ice crystal formation can damage the structure of the active substance and alter the formulation. A pen that has been frozen should not be used, even after it has thawed. Contact your prescriber or pharmacist for guidance if you believe a pen has frozen.

Signs a pen may have been compromised

• It has been stored outside the fridge for longer than the leaflet allows
• It has been exposed to direct sunlight or high heat (for example, left in a car on a warm day)
• It appears to have frozen at any point
• The liquid looks discoloured, cloudy, or contains visible particles (it should normally be clear and colourless)

If any of these apply, do not assume the pen is still effective. Your prescriber or pharmacist is the right person to advise you. Decisions about whether to use a pen that may have been temperature-affected belong with your healthcare professional — not something to guess at.

Alongside proper storage, staying consistent with your schedule matters too. You may find it helpful to read about what happens if you miss a week of Mounjaro, or about using Mounjaro after 30 days once a pen has been opened.

One of the most practical things you can do to protect your supply is keep a clear record of each pen: when you opened it, where it has been stored, and when you used it. GLP Trackr's dose logging feature lets you record every injection — date, time, and dose strength — so you always know exactly when each pen was opened and how long it has been in use. That record is especially useful if you ever need to check whether a pen is still within its permitted out-of-fridge window, or to share an accurate timeline with your prescriber or pharmacist if something seems off.

The app also sends gentle dose reminders, which helps you avoid the scenario of a pen sitting forgotten at room temperature for longer than intended. And if you do need to discuss a storage concern with your prescriber, the injection log gives you a precise history to bring to that conversation — far more useful than trying to recall dates from memory.

For a broader understanding of how this medicine works and how tracking supports your journey, take a look at our guide to how Mounjaro works. It is also worth knowing what to do if your schedule is disrupted — for example, what happens if you take Mounjaro a day early.

If you have any doubt about whether a pen is safe to use after a storage issue, contact your prescriber or pharmacist promptly — do not use the pen on the assumption it is fine. GLP Trackr supports your tracking and record-keeping; it is not a substitute for professional advice about your medicine.

Keep a clear injection history and never lose track of a pen's timeline — download GLP Trackr on the App Store or Google Play and start a free 7-day trial.