When experiencing hot weather, most of us know the importance of drinking plenty of water, trying to stay cool and wearing sunscreen. But did you know that high temperatures can also affect the way your body responds to certain medications? Some medicines can make it harder to stay hydrated, reduce your body’s ability to cool itself or increase your sensitivity to the sun. Understanding these risks can help you stay safe and well throughout the summer or when travelling to hot countries.

For most people, medicines can continue to be taken safely despite the heat. However, understanding how hot weather affects the body and how certain medicines may influence this, is an important part of protecting your health.

Never stop taking any prescribed medication without first speaking to your GP or pharmacist.

How does hot weather affect your body?

Your body works hard to keep its core temperature at around 37°C. When you become too warm, it cools itself by: 

• Sweating, which allows heat to evaporate from the skin. 
• Increasing blood flow to the skin, helping heat escape from the body. 
• Triggering thirst, encouraging you to replace fluids lost through sweating. 

During prolonged periods of hot weather, or if you are unable to replace the fluids you lose, your  body can struggle to keep cool. This can lead to dehydration, heat exhaustion and, in severe cases, heatstroke.

Older adults, babies and young children, pregnant women and people with long-term health conditions are particularly vulnerable during periods of extreme heat. 

How can medication affect your body’s response to heat?

Some medicines can make it more difficult for your body to regulate its temperature or maintain the right fluid balance. Others may increase your sensitivity to sunlight or become less effective if they are not stored correctly in hot conditions.

This does not mean that these medicines are unsafe to take when the weather is hot. It simply means you may need to take extra precautions during periods of hot weather.

If you are concerned about your medication, speak to your pharmacist or GP for advice.

Medicines that may increase heat-related risks

Diuretics (water tablets)

Diuretics are commonly prescribed for conditions such as high blood pressure, heart failure and fluid retention.

These medicines help the body remove excess fluid through urine. During hot weather, when you are already losing water through sweating, they may increase the risk of dehydration if you are not replacing enough fluids.

Medicines for high blood pressure and heart disease

Some medicines used to treat high blood pressure and certain heart conditions (including ACE inhibitors, beta-blockers and calcium channel blockers) may make it harder for your body to regulate its temperature or maintain blood pressure during very hot weather. Some can also blunt your natural sense of thirst, so you may not feel as thirsty as you should even when you need fluids.

If you become dehydrated, you may experience:

• dizziness
• light-headedness
• weakness
• fainting
• reduced urine output

Seek medical advice if these symptoms develop or become worse.

Medicines that reduce sweating

Some medicines can reduce the body’s ability to sweat normally. As sweating is one of the body’s main cooling mechanisms, this may make it more difficult to regulate body temperature during hot weather.

Examples include some medicines used to treat:

• bladder conditions
• Parkinson’s disease
• certain mental health conditions

Medicines that increase sensitivity to sunlight

Some medicines can make your skin much more sensitive to ultraviolet (UV) rays, increasing the risk of sunburn. Common examples include certain antibiotics, diuretics, antidepressants, antipsychotics and some treatments for acne or eczema.

If your medicine causes photosensitivity, the patient information leaflet supplied with your medication will usually include a warning.

Extra precautions include:

• applying a high-factor sunscreen
• wearing loose, protective clothing
• seeking shade during the hottest part of the day
• avoiding prolonged exposure to direct sunlight

Looking after your medicines in hot weather

Hot weather can affect medicines as well as people. High temperatures can alter how a medicine works or how quickly it’s absorbed, so it’s worth taking extra care with storage in higher temperatures. Most medications state to store below 25 degrees. 

Always check the storage instructions supplied with your medication. Most medicines should be stored in a cool, dry place away from direct sunlight. Being exposed to higher temperatures can reduce the effectiveness of some medication and may even change its formulation.

Avoid:

• leaving medicines in a hot car (bring a cool bag)
• storing medicines in bags or on windowsills that catch the sun
• exposing medicines to excessive heat

Some medicines, such as insulin, have specific storage requirements. Follow the manufacturer’s instructions carefully and ask your pharmacist if you are unsure. If you have medicine that you need to carry around with you (such as an Epipen or asthma pump) ideally keep these in a small cool bag and ensure you don’t leave them in a hot car or room for any extended period.

What if I have left my medicine in the heat?

If your medicine has: 

• Changed colour 
• Developed a strange smell
• Changed in texture 
• Or appears different

This could be a sign of damage and you should seek advice from your pharmacist. 

How Heat Can Affect Medical Devices

It’s not just medicines that need protection during hot weather. High temperatures and humidity can also affect some medical devices, making them less reliable or reducing how well they work.

Devices such as insulin pumps, blood glucose monitors and blood glucose test strips can become less accurate if they are exposed to excessive heat. Heat may also affect the batteries and electronic components inside some devices.

Medical devices that deliver medication, including insulin pumps and some inhalers, can also be affected. High temperatures may reduce the effectiveness of the medicine they contain, meaning the correct dose may not be delivered.

To help keep your medical devices working properly:

• Follow the manufacturer’s storage and operating temperature guidance.
• Keep devices out of direct sunlight and avoid leaving them in hot cars or bags.
• Store test strips and other accessories according to the instructions on the packaging.
• If you think your device or medication has been exposed to excessive heat, or it isn’t working as expected, seek advice from your pharmacist, healthcare team or the device manufacturer before continuing to use it.

Taking a few simple precautions can help ensure your medical devices continue to work safely and effectively throughout the summer.

If you are worried that your device is not working correctly you should visit the MHRA website or report any concerns through the MHRA’s Yellow Card scheme.

Travelling with Medicines in Hot Weather

If travelling abroad, pack all essential medication and medical supplies in your hand luggage to prevent loss or delays, but keep extra supplies in your hold luggage. Leave all medicines in their original packaging with pharmacy labels, and bring a copy of your prescription and a doctor’s letter detailing your specific health conditions.

Before you travel, check the storage instructions for your medicines and any medical devices you use. Keep them out of direct sunlight, avoid leaving them in parked cars or hot luggage compartments whenever possible, and store them in a cool, dry place once you reach your destination. If a medicine needs to be refrigerated, plan ahead so you can keep it within the recommended temperature range during your journey. 

If you’re unsure whether your medicine or medical device has become too hot, or you think it may not be working properly after being exposed to high temperatures, speak to a pharmacist or your healthcare team before continuing to use it.

Taking a few simple precautions before and during your holiday can help ensure your medicines and medical devices remain safe and effective wherever your summer takes you.

About Us

First Aid for Life provides this information for guidance and it is not in any way a substitute for medical advice. First Aid for Life is not responsible or liable for any diagnosis made, or actions taken based on this information. It is strongly advised that you attend a practical First Aid course to understand what to do in a medical emergency.

First Aid for Life offer tailored first aid courses for specific activities and destinations.

Written by Emma Hammett from First Aid for life
www.firstaidforlife.org.uk

It is strongly advised that you attend a Practical First Aid course to understand what to do in a medical emergency. Please visit www.firstaidforlife.org.uk  and www.onlinefirstaid.com for more information about our practical and online courses and to access free resources.

First Aid for life provides this information for guidance and it is not in any way a substitute for medical advice. First Aid for Life is not responsible or liable for any diagnosis made, or actions taken based on this information.

Author: Emma Hammett