What to know if your Mounjaro pen is exposed to heat

It’s the middle of summer. You get home after work to find your Mounjaro (tirzepatide) delivery left outside, baking in the sun. Should you inject it or throw it away? It’s a question many people are asking. As more people start using GLP-1 medications like Mounjaro for weight management or diabetes, the logistics of keeping it cool, especially in warmer months, start to become a real headache.

We’re unpacking what happens when Mounjaro gets too warm, what you can do to prevent it, and when it’s time to reach out for support.

Why heat and Mounjaro don’t mix

Like many injectable medicines, Mounjaro contains delicate proteins. These proteins need to be stored in a fridge (between 2°C and 8°C) to stay effective.¹ If they’re exposed to high temperatures for too long, they can start to break down, and that doesn’t necessarily affect its safety, but means the medicine might not work properly.²

You should never freeze Mounjaro, but you can store it outside the fridge for up to 30 days, provided the temperature stays under 30°C.¹ Once temperatures go above that, like when your parcel is left in direct sunlight or a hot delivery van, you’ll need to double check your medication to make sure it’s still fine to take.

What happens if Mounjaro gets too warm

Heat exposure doesn’t always show up in obvious ways, but here are a few warning signs you can look out for:

• The solution inside the pen may become cloudy, discoloured, or develop floating particles

• The pen itself might feel warm or even hot

• You might also notice your dose isn’t working as well as usual

Mounjaro is designed to handle short periods of time out of the fridge, and a bit of warmth won’t instantly spoil it. Like any medication, exposing Mounjaro to heat for a longer time might make it less effective, but that doesn’t mean it isn’t safe to administer.

However, if you’re concerned about a delivery being left out in the heat longer than expected, there may be a slight chance that the heat will affect the effectiveness of your medication.

To counteract this, all Mounjaro pens being delivered come in a sealed envelope, in which there are cooling bags to help regulate the temperature. If, for any reason, your pen doesn’t arrive in an enclosed envelope with any cool bags, then reach out to [email protected] for further advice.

How to check if your Mounjaro is safe

There are a few ways to check whether your pen is safe to use:

1. First, feel the pen. It should be cool to the touch. Not warm, and certainly not hot. 

2. Inspect the liquid inside. It should be clear and colourless. Any cloudiness or visible particles are a sign that the pen should not be used.

3. Check the packaging. Is the cool pack still cold enough to keep the medication from being heated?  If not, then take the pen out of the box and check to see if the pen itself is still at a relatively ‘normal’ temperature.

If in doubt, contact Numan’s Customer Care team using [email protected]. It’s better to check than risk using a compromised pen.

What to do if you left Mounjaro out of the fridge

We’ve all forgotten to put things back in the fridge. If that happens with Mounjaro, the action you take depends on how long it was left out and the temperature of the environment:

• If it was left out for under two hours at room temperature (below 30°C), it’s still safe. Just return it to the fridge.¹

• If it’s been at room temperature for up to 30 days, it’s also fine, but make a note of the date.¹

• After 30 days outside the fridge, even if it’s been kept cool, the pen must be discarded.

• If it was exposed to heat above 30°C for several hours, such as being left in a hot car, a sunny windowsill, or during a delivery delay, it may no longer be safe to use.¹ In this case, contact Numan for guidance.

How to prevent this in future

There are a few easy ways to reduce the risk of heat exposure. 

1. Always track your delivery and bring it inside as soon as possible. 

2. Store your pens in the fridge immediately and avoid placing them near heat sources like ovens or radiators.

3. If you’re travelling or going somewhere without reliable refrigeration, consider using a medical-grade cooling case.

During summer, these steps can help mitigate any potential issues you may come across. If there’s ever a power cut or fridge failure, having a backup cool storage method on hand can also help.

The numan take

Mounjaro can be a great tool to help you on your weight loss journey, but only if stored correctly. If your pen has been exposed to heat, looks unusual, or you’re unsure whether it’s still safe to use, do not take the risk. Contact Numan’s Customer Care team ([email protected]) for support. We’re here to help you stay on track with treatment and ensure your medication is both safe and effective.

References

1. ^{Mounjaro KwikPen 10mg solution for injection in pre-filled pen. Org.uk. https://www.medicines.org.uk/emc/product/15484/smpc [Accessed 25th June 2025].}

2. ^{Bjarnason J, Carpenter KJ. Mechanisms of heat damage in proteins. 2. Chemical changes in pure proteins. The British journal of nutrition. 1970;24(1): 313–329.}