Do you put Mounjaro in the fridge — and what happens if you don't?

Step 1, Keeping pens refrigerated before you use them

From the moment your Mounjaro arrives, the pens go straight into the fridge. The licensed temperature range is 2–8°C, which is standard fridge territory. Most household fridges sit in this range on the middle or lower shelves; the fridge door stays a little warmer and experiences more temperature swings, so the middle shelf is a safer home than tucking them next to the butter in the door rack.

Keep each pen inside its original carton. Tirzepatide is light-sensitive, and the packaging is part of the protection. The cap stays on when the pen is not in use. These are not complicated rules, but they matter: a pen stored incorrectly may not deliver the dose reliably, and you would have no way to tell by looking at it.

If you have questions about storage when you first start treatment, our clinical team is available to answer them as part of the aftercare included with every prescription. You can also find general guidance on what starting treatment involves on the Mounjaro injection overview.

Step 2, Taking the pen out of the fridge for your weekly dose

Most people find that injecting with a pen that has been sitting at room temperature for 30 minutes or so is more comfortable than injecting straight from the fridge; cold liquid can sting more on the way in. If you want a fuller answer to whether Mounjaro has to be kept in the fridge at all times, including when brief room-temperature periods are acceptable, that page covers it in detail.

Once the pen is out of the fridge, there is a defined window during which it remains fit for use at room temperature. That figure is printed in the Patient Information Leaflet that comes in the box, and the NHS tirzepatide medicines page also carries storage guidance. Read both; do not rely on approximate figures circulating online, including any that appear in body text on this site. Product information is the authoritative source.

If you are not ready to inject at the time you removed the pen, you can put it back in the fridge, provided the room-temperature limit has not been reached. There is more detail on this specific question, including what the SmPC says about returning pens to cold storage, on the can I put Mounjaro back in the fridge page.

Step 3, Situations where storage goes wrong and what to do

A few things can disrupt your storage routine. Freezing is the most serious. If a pen has been frozen (left in the freezer compartment by mistake, or placed near a freezer vent in a fridge set too cold) it must not be used. Frozen and then thawed pens should be discarded safely. A sharps container is the correct way to dispose of any used or damaged pen.

Power cuts are a common concern. If your fridge was off for a short period and the pens stayed visibly cold (the food around them was still cold), you are likely within the room-temperature window and normal rules apply. If the fridge was off long enough that the interior reached room temperature, count from that point using the window in your leaflet. When in doubt, contact your prescriber or the pharmacist who dispensed your pens rather than guessing.

Travel is another common scenario. Taking a pen on a flight, to a hotel, or to a gym bag mid-holiday is fine within the room-temperature limit. Insulated pouches can help in warm climates, but they are not a substitute for knowing the limit. If you are planning a longer trip, it is worth raising storage logistics with your prescriber in advance.

A word on why storage matters for a medicine like this

Tirzepatide is a peptide medicine. Like many biological drugs, its structure can degrade when exposed to temperatures outside the licensed range, light, or physical damage. A degraded pen may look identical to an intact one. That is why the storage rules exist and why following them carefully is part of getting the most from your treatment.

It is also one of the reasons that sourcing matters. Pens that have been stored correctly throughout the supply chain, dispensed by a GPhC-registered pharmacy, and delivered in temperature-controlled conditions arrive in the state the manufacturer intended. Pens sold through unverified channels may have spent unknown periods outside the correct storage range, and if you are researching whether a generic tirzepatide injection is available as an alternative, that page explains where things currently stand and what to be aware of.

If you are exploring Mounjaro for weight management, the Mounjaro overview covers how the medicine works and what clinical trials found. For context on what private treatment costs and what that price includes, the Mounjaro price page sets it out plainly. And if you are ready to find out whether treatment is appropriate for you, check your eligibility with our prescribers, the consultation is free, and a named clinician reviews every application the same day.