How Long Does One Mounjaro Pen Last?

Mounjaro (tirzepatide) is supplied as a single-use, pre-filled pen. Each pen holds one dose at a fixed strength — commonly available at 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, or 15 mg — and is designed to deliver that dose in a single weekly injection. There is no reservoir to draw from across multiple weeks; one pen equals one dose equals one week.

Unopened pens: how long do they last?

Unopened Mounjaro pens have a shelf life set by the manufacturer. As a general guide, they are typically stored in the refrigerator and remain usable until the expiry date printed on the label — but always check the patient information leaflet that came with your specific pen, or refer to the electronic Medicines Compendium (eMC) for the precise figure. Do not use a pen beyond its printed expiry date. For a closer look at how long an unopened Mounjaro pen remains usable, that page covers the details in full.

Storing your pen in the fridge

Unopened pens should be kept refrigerated (between 2°C and 8°C) until you are ready to use them. They can also be kept at room temperature for a limited period — your leaflet will state the maximum duration for out-of-fridge storage, which is typically a matter of weeks rather than months. Check the leaflet for the exact window. For guidance specifically on storing your Mounjaro pen in the fridge, including what to do if your pen has been left out, that page has more detail.

After use

Once you have administered your injection, the pen has done its job. It should not be reused or kept for another dose. Follow your prescriber's or local waste-disposal guidance on how to discard used sharps safely.

For a fuller breakdown of how long a Mounjaro pen lasts across different scenarios, or to explore what one pen of Mounjaro covers in terms of your weekly schedule, those pages go into further detail.

Knowing when you used your last pen — and when your next one is due — is where GLP Trackr's dose logging feature is most useful. Every time you administer an injection, you can log the date, time, and dose strength directly in the app. That creates a running record so you can see at a glance exactly where you are in your weekly schedule, without relying on memory.

Alongside dose logging, the app's reminder feature means you will receive a gentle nudge when your next weekly injection is due — helping you avoid accidentally going longer than intended between doses. If you do miss a dose, the app lets you log that too, giving you something concrete to discuss at your next appointment rather than trying to reconstruct your history from memory.

Staying consistent week on week is one of the most important parts of a GLP-1 journey, and having a clear log makes that easier to maintain. You can also find broader context on how Mounjaro works if you want to understand more about the medicine you are already taking.

If you are ever unsure whether a pen has been stored correctly, or whether it is still safe to use, contact your prescriber or doctor — they can advise based on your specific situation. GLP Trackr records your journey and helps you prepare for those conversations; it is not a substitute for professional guidance.

Ready to log your doses and stay on top of your weekly schedule? GLP Trackr is free to try for 7 days — available on the App Store and Google Play.