Can I use my Mounjaro pen after 30 days out of the fridge?

Step 1: understand when the 30-day clock actually starts

A question our prescribers hear most weeks is whether the 30 days begins at the first injection or the moment the pen is taken out of the fridge. The answer is the latter. As soon as the pen is removed from refrigerated storage, the countdown begins, even if you put it back in the fridge the same afternoon and used it from the fridge again the following week. That brief spell at room temperature counts toward your total. The Mounjaro SmPC on the eMC is the authoritative reference for these conditions, and your Patient Information Leaflet carries the same guidance in plain language.

Before that first removal, the pen is stable in the fridge at 2–8°C for the full shelf life shown on the label. Many people find it easiest to keep all unused pens refrigerated and only bring one out when they are ready to use it. If you would like a practical walkthrough of using your Mounjaro pen after 30 days have elapsed, including what the guidance means for your routine, that page sets out the detail clearly.

For a fuller look at what the storage rules mean in practice, the page on Mounjaro storage after 30 days in the fridge covers the question in detail.

Step 2: check the temperature, not just the calendar

Time is only half the picture. The pen must also be kept below 30°C throughout its time out of the fridge. On a warm summer day, a pen left on a windowsill, in a car glovebox, or near a radiator could reach that threshold well before 30 days have passed. If there is any reason to think the pen has been exposed to heat above that limit, you should not use it, contact your prescriber or pharmacist for advice before proceeding.

This matters because protein-based medicines like tirzepatide can degrade when exposed to heat, and that degradation is not always visible. The liquid may still look clear and colourless even if potency has been affected. This is exactly why the storage limits in the SmPC exist: they reflect stability data from controlled testing, not a conservative guess. The NHS medicines page for tirzepatide also points readers to the leaflet for storage detail, reinforcing that these instructions are non-negotiable.

If you are travelling or carrying your pen during the day, a cool bag or insulated pouch keeps the temperature stable. Avoid storing it in direct sunlight or in a hot car.

Step 3: decide what to do if the 30 days has passed

If you realise your pen has been out of the fridge for more than 30 days, do not use it. Even if doses remain, the storage window has closed and the medicine should be treated as expired. Continuing to inject from a pen that has exceeded its room-temperature limit carries an unknown risk: the dose you receive may be lower than intended, and the clinical outcome will not match what your prescriber planned for you.

Dispose of the pen in a sharps container and contact your provider to discuss a replacement. If you are managing your treatment through nume, our prescribers are available seven days a week to advise on the next step, including whether a dose needs to be reconsidered in light of a missed or voided injection.

For related detail on what actually happens if the pen is used beyond this point, the page on using Mounjaro after 30 days covers the clinical reasoning. And if you are thinking about how to plan ahead so this situation does not arise again, the overview of how the Mounjaro injection works is a useful starting point alongside your leaflet.

Practical habits that prevent the problem

The simplest approach is to write the removal date on the pen with a marker the moment it comes out of the fridge. Thirty days from that date is your hard deadline. If your weekly injections fall on the same day each week, a pen containing four doses should be used up in about 28 days from first removal, giving you a small buffer before the limit arrives.

Some people on a treatment programme manage more than one pen at once, perhaps because they receive a month's supply. Keep any pen you are not yet using in the fridge until the previous one is finished. This also means that if your schedule shifts (a holiday, an illness, a delayed injection) the spare pen's clock has not yet started. The page on what to do with your Mounjaro pen after injection explains the needle and recap steps that form the routine around each dose.

Mounjaro is a prescription medicine for weight management, available through a registered pharmacy following a clinical assessment. If you are not yet on treatment and want to understand the full process (including eligibility and what a private prescription involves) our treatment consultation page is the right place to start. You can also read a broader overview of Mounjaro for weight loss in the UK or explore weight-loss treatment options more generally.