How Long Can Tirzepatide Stay in the Fridge?

What the SmPC tells us, and why those numbers exist

The storage rules for tirzepatide come directly from stability testing carried out during the licensing process. Manufacturers expose the medicine to a range of temperatures and measure how the active molecule degrades over time. The results set the permitted storage window, and those windows are published in the Mounjaro SmPC on the eMC: 2–8°C in the fridge, protected from light, not frozen. Within those conditions, the pen remains stable until the expiry date printed on the label.

What the SmPC also specifies (and what is worth reading carefully before your first pen arrives) is the maximum period the pen may spend outside the fridge at room temperature. That figure is stated precisely in the leaflet included with your pen. We deliberately do not print it here, because the out-of-fridge window can differ between product batches and any update to the SmPC would make a hardcoded number misleading. The leaflet that comes with your pen, and the eMC page, are the places to check.

One practical thing the data makes clear: the out-of-fridge period is cumulative. If you take the pen out for an hour, put it back, then take it out again a week later, those hours count together, and our page on how long Mounjaro can stay out of the fridge explains exactly why that running total matters. The pen does not reset every time it returns to the fridge.

For a broader look at what happens when a pen spends time outside refrigeration, the out-of-fridge guidance page covers the detail.

Where in the fridge to put it, and where not to

A household fridge does not keep the same temperature throughout. The door shelves are warmest, cycling between ambient and set temperature every time the door opens. The freezer compartment and the shelf directly beneath it can dip below 0°C. Both are wrong for tirzepatide. The middle shelves, away from the door and away from the back wall (where ice can form), are the most stable zone.

Keep the pen in its original carton. The carton protects against light exposure, which is a separate degradation pathway from temperature. It also makes it easier to check the expiry date at a glance without handling the pen unnecessarily.

One situation that catches people out: ordering around a bank holiday or a week you are not at home. If your pen is dispatched on a Friday and sits in a warm parcel locker over a long weekend, the out-of-fridge clock has been ticking since dispatch. Our tirzepatide fridge storage guide covers transit and delivery scenarios in more detail. It is worth planning your orders so the pen arrives when you are around to put it straight in the fridge, a consideration that is easy to overlook when payday, a Monday order slot and a school half-term all coincide.

Never use a pen that has been frozen. The medicine cannot be recovered by thawing, and there is no visible sign that damage has occurred.

How fridge storage fits into safe, supervised treatment

Storage is one part of using tirzepatide safely and correctly, but it sits within a wider picture of clinical oversight. The NHS patient information page for tirzepatide covers storage alongside side effects, missed doses, and when to seek urgent medical advice, a useful complement to the information in your pen's leaflet.

Treatment with Mounjaro starts at 2.5mg, a dose chosen to help your system adjust, and is titrated over time by your prescriber. How you store each pen between doses is part of that prescriber's responsibility to advise on, and our clinical team is available seven days a week if a storage question comes up mid-cycle. A named prescriber, not an automated system, reads every consultation at nume.

If you are thinking about cost alongside storage (pens do have a finite out-of-fridge life, which affects how you plan travel and holidays) the context around how Mounjaro is priced in the UK is worth reading before you decide how many pens to order at once. Ordering more than you will use within the fridge window is something our prescribers flag during review, and if you are unsure how that window works in practice, our guide to how long you can keep tirzepatide in the fridge sets out the full picture.

For injection technique questions that sit alongside storage (rotating sites, changing needles) the Mounjaro injection guidance page covers those steps. Clean technique and correct storage work together; neither is the whole picture on its own.