Keeping Mounjaro in the fridge after first use: what the SmPC actually says

Step 1, Collect and unbox your pen

Your Mounjaro pen arrives via DPD in plain, unbranded packaging with a tracking notification, so you know exactly when to be in. The cold-chain box is designed to keep the pen within the required temperature band during transit. As soon as it arrives, move the pen straight to your fridge, the vegetable drawer or a middle shelf works well, away from the back wall where temperatures can dip low enough to risk freezing. Never place a Mounjaro pen in the freezer compartment, even briefly. A frozen pen must not be used.

Check the pen is intact and that the liquid visible through the window is clear and colourless before your first injection. Discolouration or visible particles are reasons to contact your prescriber or our aftercare team before proceeding.

If you want a broader overview of what Mounjaro is and how it works, the Mounjaro treatment page covers the mechanism, eligibility and what to expect from treatment.

Step 2, After your first injection, return the pen to the fridge

One of the most common questions our prescribers hear is whether a started pen still needs refrigerating. It does. The pen goes straight back into the fridge after each weekly dose, and if you are unsure about the detail, our guide on how to store Mounjaro after first use walks through exactly what to do. Store it at 2–8 °C for the remaining three doses, capped correctly with the outer needle cover removed and replaced with the pen cap.

The NHS patient information for tirzepatide confirms the cold-storage requirement and describes the conditions under which a pen may be kept at room temperature for a limited period, for instance if you are travelling and a fridge is not accessible. Crucially, the leaflet specifies the maximum number of days and temperature ceiling that apply during any room-temperature period. NHS guidance on tirzepatide directs patients to the Patient Information Leaflet for these figures; we do the same, because citing a specific number of days here when your leaflet is the governing document would be unhelpful.

For a detailed read of the storage section, the Mounjaro SmPC on the eMC sets out the full storage conditions as agreed with the regulator. That is the authoritative source.

Step 3, Handling and needle safety between doses

After injecting, remove and dispose of the needle before recapping the pen. Leaving a needle attached creates a path for air and contaminants to enter the cartridge, and reusing a needle risks injection-site reactions and inaccurate dosing. A dedicated sharps container makes needle disposal straightforward and legally compliant, you cannot put used needles in household recycling or general waste.

Clean the injection site with an alcohol swab beforehand and rotate sites between the abdomen, thigh and upper arm. Rotating prevents the kind of hardened tissue that develops at a repeatedly used spot and can affect how consistently the medicine is absorbed.

When the pen is empty, it should not go in the household bin either. Details on how to return or recycle used Mounjaro pens are on our pen recycling page.

What to do if your pen has been left out of the fridge

Life happens. A pen accidentally left on the kitchen counter overnight is a situation worth handling calmly rather than catastrophically. The key question is how long it was out and at what temperature, both figures matter, and the Patient Information Leaflet gives you the threshold. If the pen was within the room-temperature window specified in the leaflet, it can generally be used. If it exceeded that window, contact your prescriber before injecting.

The same logic applies if the pen was exposed to direct sunlight or high heat. Do not use a pen that looks discoloured or cloudy. Our FAQs cover several common pen-handling scenarios, and if yours is not there, our team is available seven days a week.

For anyone thinking about starting Mounjaro and wondering about whether you keep Mounjaro in the fridge as part of that decision, our weight-loss treatment overview sets out how the process works from consultation through to delivery and ongoing support. You may also find it helpful to read about whether you store Mounjaro in the fridge after first use and whether you keep your Mounjaro pen in the fridge throughout your treatment.