How long does Mounjaro last in the fridge?

Unopened, it keeps in the fridge (2 to 8 °C) until the expiry date printed on it; do not freeze it. Once you have started a pen, it can be kept in the fridge or below 30 °C for up to 30 days, then it should be discarded.

I left my pen out overnight. Is it still OK?

If it stayed below 30 °C, an overnight spell is well inside the in-use window for all of these pens, so put it back in the fridge and carry on. If it got hot, such as in a car or in direct sun, replace it to be safe.

No. Freezing damages the medicine, and a pen that has been frozen should not be used, even once it thaws. Keep it away from the freezer compartment and the coldest part of the fridge.

Do I count the in-use days from when I take it out of the fridge, or from the first injection?

From when the pen first comes out of the fridge to be used. Write the date on the pen or on your calendar so you can count the days and know when to discard it.

How to store Mounjaro and Wegovy pens

Keep it in the fridge, do not freeze it, and once you start a pen it only lasts a set number of days out of the fridge. Here are the exact limits from each pen's UK leaflet, and what to do if yours got warm.

Last updated 3 November 2026

The short version

Unopened: keep it in the fridge, 2 to 8 °C, until the expiry date. Do not freeze.
In use: it can be kept below 30 °C for a set number of days, then must be discarded (Mounjaro 30 days, Wegovy 6 weeks).
Never freeze it. A pen that has been frozen should not be used.
Not sure if yours is still good? Use the storage checker.

Before you start: keep it in the fridge

An unopened pen keeps in the fridge at 2 to 8 °C until the expiry date on the label. Store it in the main body of the fridge, not the door (where the temperature swings) and not against the back wall or in the freezer compartment, where it could freeze. Keep the cap on and the pen in its box, out of the light.

Once in use: the in-use window

When you take a pen out of the fridge to use, the manufacturer sets a limited time it can be kept below 30 °C before you must throw it away. The window is different for each pen:

Pen	Unopened	In use
Mounjaro (KwikPen)	Fridge until expiry	up to 30 days below 30 °C
Wegovy (FlexTouch)	Fridge until expiry	up to 6 weeks (42 days) below 30 °C
Ozempic	Fridge until expiry	up to 6 weeks (42 days) below 30 °C
Saxenda	Fridge until expiry	up to 30 days below 30 °C

Write the date the pen first left the fridge on the pen or your calendar, so you can count the days. Your own leaflet is the final word, since limits can differ by strength and pack.

Never freeze it

Freezing damages these medicines. A pen that has been frozen must not be used, even after it thaws and looks normal. That is why the freezer compartment and the coldest shelf are the two places to avoid.

If it got warm, or you are not sure

A short spell below 30 °C, even overnight, is inside the in-use window for all of these pens, so refrigerate it and carry on. If it sat somewhere hot, a car in the sun or a windowsill, the dose cannot be relied on, so most people would start a new pen. Our storage checker gives you a straight keep or bin answer for what happened to yours.

Travelling with it

The in-use window is what gives you room to travel. For flights, temperature and the needles, travelling with a weight loss pen covers it.

Common questions

How long does Mounjaro last in the fridge?: Unopened, it keeps in the fridge (2 to 8 °C) until the expiry date printed on it; do not freeze it. Once you have started a pen, it can be kept in the fridge or below 30 °C for up to 30 days, then it should be discarded.
I left my pen out overnight. Is it still OK?: If it stayed below 30 °C, an overnight spell is well inside the in-use window for all of these pens, so put it back in the fridge and carry on. If it got hot, such as in a car or in direct sun, replace it to be safe.
Can I freeze my pen?: No. Freezing damages the medicine, and a pen that has been frozen should not be used, even once it thaws. Keep it away from the freezer compartment and the coldest part of the fridge.
Do I count the in-use days from when I take it out of the fridge, or from the first injection?: From when the pen first comes out of the fridge to be used. Write the date on the pen or on your calendar so you can count the days and know when to discard it.

Sources

Storage limits are from each product’s UK SmPC as of 3 November 2026, and can differ by strength and pack. Always follow the leaflet in your own pack. This is general guidance, not medical advice.