How to keep your medicines safe during hot weather

Why heat can damage medicines

Medicines are more sensitive to temperature than people may realise. Many are designed to be stored below 25°C, ideally between 15°C and 25°C. Specific storage requirements, such as refrigeration (between 2°C and 8°C), will be listed on the packaging.

Above 25°C, the chemical structure of some medicines can begin to break down. This can affect how well the medicine works.

Excessive heat can also cause creams to separate, liquids to evaporate, or capsules to melt. The UK’s drugs regulator, the Medicines and Healthcare products Regulatory Agency, warns that heat can affect tablets, inhalers, insulin and other everyday treatments.¹

Which medicines are most affected by hot weather?

Insulina is a protein, and proteins can change shape when exposed to heat. Once this happens, the medicine may not work effectively, and some research shows that insulin loses potency as temperatures rise.² This is why manufacturers recommend keeping unopened insulin in the fridge and using opened pens or vials only at room temperature for a limited time.

The same is true for GLP-1 medicines, such as Wegovy y Mounjaro. These are used for type 2 diabetes and weight management. Like insulin, they are protein-based medicines, meaning they can break down when exposed to heat and are less likely to be effective. Manufacturers advise keeping GLP-1 pens in the fridge before use and storing them below 30°C once opened.³

Other medicines are also at risk. Inhaladores contain gases that can expand in heat, affecting how much medicine is released or causing the inhaler to burst.

A study looking at salbutamol inhalers in real-life summer conditions (often reaching 40°C) delivered up to 12% less salbutamol and produced larger aerosol particles.⁴ This means less drug reaches the lungs, so patients may receive less relief from their asthma symptoms.

Even medical devices, such as blood glucose monitors, can be affected. A study showed that short bursts of high heat (42°C) and humidity (83% relative humidity) caused glucose meters and strips to give falsely high readings, sometimes by 30% within just 15 minutes.⁵ Even brief exposure can lead to unsafe overestimation of glucose.

Where medicines are more likely to overheat

The problem is that medicines often overheat in everyday places. Cars are one of the worst locations, as a parked vehicle can reach more than 40°C on a warm day. Windowsills are another danger because direct sunlight can heat medicines far beyond the temperature of the room.

Research estimates that around half of UK homes now overheat (indoor temperatures above 26°C) during heatwaves, especially older buildings that trap warm air.⁶

Bathrooms are also risky, as humidity and sudden temperature changes can affect both medicines and devices. Research shows that people commonly store medicines in kitchens and bathrooms, where temperature and humidity fluctuate.⁷

Sustained heat exposure is the real concern. Many medicines may tolerate brief periods of warmth, but several days of high temperatures, especially during a heatwave, increase the chance of chemical breakdown and loss of potency.

Keeping medicines safe during hot weather

There are ways to protect medicines during hot weather.

• Avoid storing medicines in bathrooms or kitchens where temperatures change quickly. A room thermometer can be useful. Keep it in the coolest part of the house and away from sunlight. However, even this may not be enough in some homes that overheat.

• Closing the curtains or blinds, windows and using fans in the room may help. With persistent heatwaves, it may be worth investing in air conditioning to protect medicines – even a portable option for one room. Currently only around 19% of households in Great Britain have air conditioning.

Travelling requires extra planning. Medicines can also get hot in pockets and bags, so they should be carried in insulated pouches or cool bags. They should not be placed directly next to ice packs, as freezing can be just as damaging as heat. Never leave medicines in a parked car.

Know the signs of damaged medicines

It is also important to know the signs of heat-damaged medicines. Tablets may become soft, crumbly or discoloured. Liquids may look cloudy or have crystals. Inhalers may feel warm or deliver weaker doses.

Any change in appearance or performance should be checked with a pharmacist. For insulin and GLP-1 users, unexplained high blood sugar readings may be a sign that the medicine has been damaged.

Heatwaves may feel like a welcome break from the usual British drizzle, but they bring hidden risks for medicines. As temperatures rise, protecting your medicines becomes just as important as protecting your skin. Keeping them cool, checking for changes and avoiding direct sunlight can help ensure they work exactly as they should.

This article is republished from The Conversation under a Creative Commons license. Read the original article.