My Mounjaro Pen Is Stuck — What to Do

Before assuming the pen is faulty, it is worth working through a few of the most frequently reported causes. Many people find the issue is straightforward once they know what to look for.

The pen has not been primed

If you have not yet completed the priming step, the pen may not activate correctly. Priming clears any air from the needle and confirms the pen is ready to use. If you are unsure whether your pen has been primed, check the instructions that came in the box — or read about how to prime a Mounjaro pen for a general overview of the process.

The pen is too cold

Mounjaro pens are stored in the refrigerator, and a pen that has just come out of the fridge can feel stiff or resistant. Check the leaflet that came with your pen, but it is generally advised to let the pen sit at room temperature for a period before use — typically around 30 minutes, though your own pen's instructions are the definitive guide.

The needle cap is still attached or not fully seated

If the needle has not been properly attached, or the cap has not been fully removed before use, the pen may not depress as expected. Work through each step of the preparation process carefully, as described in your Patient Information Leaflet.

The pen is jammed or has a manufacturing defect

Occasionally, a pen may have a genuine mechanical problem. If you have checked the above and the Mounjaro pen is still jammed after following all preparation steps, do not force it. Contact your pharmacist or the pen's manufacturer. Details for reporting a suspected product defect are usually included in your pack or available from your pharmacist — you can also report concerns through your national reporting scheme (such as the UK's Yellow Card scheme).

For more general information about the pen device itself, the Mounjaro pen guide covers the key things to know about how it works.

When a pen issue disrupts your usual injection routine, keeping an accurate record of what happened matters more than ever. GLP Trackr's dose logging feature lets you record exactly what occurred — whether you completed the injection, had a partial dose, or had to delay — so you have a clear, dated account to share with your prescriber or pharmacist at your next contact.

This kind of record is genuinely useful: it removes any guesswork about when your last successful dose was, and gives your healthcare team the context they need to advise you. You can also set a dose reminder so that once the issue is resolved, your weekly schedule gets back on track without a second missed pen.

If you want a broader picture of your Mounjaro journey — including injection history, how you have been feeling, and your progress over time — the complete Mounjaro tracking guide brings it all together.

Start logging your doses, sites, and any pen issues in GLP Trackr — free to download on the App Store and Google Play, with a 7-day trial to explore everything.

A note on safety: if you are unsure whether you received your full dose, or if you are worried about what to do next, always contact your prescriber or pharmacist before making any decision about your injection. They know your full treatment history and are best placed to advise you — GLP Trackr helps you record what happened, but it is not a substitute for that guidance.