MHRA: Keeping Medications & Patients Safe in Extreme Heat

As the UK experiences another period of high temperatures, health officials are warning that hot weather can affect medicines, medical devices and the body's response to treatment. 

The Medicines and Healthcare products Regulatory Agency (MHRA) says heat can reduce the effectiveness of some medicines, increase the risk of dehydration and make certain people more vulnerable to heat-related illness. 

These concerns are becoming increasingly important as climate change contributes to more frequent, longer-lasting and more intense heatwaves across the UK and globally.

How heat can affect medicines and medical devices

According to the MHRA, many medicines should be stored below 25°C, yet temperatures inside cars, bags, trains, buses and rooms exposed to direct sunlight can quickly exceed this level during hot weather. 

Heat can break down active ingredients in medicines, potentially reducing their effectiveness when patients need them most. This can affect a wide range of treatments, including tablets, inhalers, hormone patches, insulin and EpiPens.

Medicines that require refrigeration, such as insulin and some liquid antibiotics, are particularly vulnerable to heat exposure. 

The MHRA advises people to check storage instructions in patient information leaflets, keep medicines in the coolest part of the home and avoid leaving them in parked vehicles or warm bags. Medical devices can also be affected. 

The MHRA notes that blood glucose monitors used by people managing diabetes may produce less reliable readings if stored or used in hot conditions.

Higher temperatures and health risks 

The MHRA warns that hot weather can alter how the body responds to medicines and increase the risk of dehydration. 

“Let’s face it – when there’s a heatwave, most of us are focused on getting outside and enjoying it while it lasts. But it’s easy to forget that medicines left in the heat – in cars, bags or on sunny windowsills – might not work properly when you need them,” says Alison Cave, Chief Safety Officer at the MHRA.

“Some medicines can also make you more likely to burn in the sun, feel dizzy or get dehydrated, especially if you’re taking diuretics or have a condition like asthma, heart disease or diabetes.

“To stay safe in the heat:

• "Store medicines somewhere cool, dry and out of direct sunlight – especially if you’re out and about
• "Know the signs of heat-related illness – stay hydrated and listen to your body
• "Take extra care in the sun if your medicine makes your skin more likely to burn

“And remember, for all medicines it’s important to read the leaflet and speak to a healthcare professional if you have any questions.”

People taking diuretics lose additional fluid through urination, while some blood pressure medicines can make it harder for the body to regulate temperature during hot spells. 

Certain diabetes medicines, including insulin and metformin, can also increase dehydration risks or make early warning signs more difficult to recognise.

Other medications, including some antipsychotics and stimulant medicines used for attention disorders, may raise body temperature and increase the likelihood of overheating. 

Symptoms of dehydration can include dizziness, headaches, tiredness, confusion and dark urine. According to the MHRA, older adults, young children and people with heart or kidney conditions may face greater risks during periods of extreme heat. 

Some commonly used medicines can make the skin more sensitive to sunlight. 

The MHRA highlights that certain antibiotics, diuretics, antidepressants and treatments for acne or eczema can increase the risk of sunburn. 

Methotrexate, which is used to treat conditions including rheumatoid arthritis, psoriasis, Crohn's disease and cancer, requires particular caution because it can cause severe skin reactions following sun exposure.

These risks become more significant as people spend more time outdoors during warm weather. 

The MHRA advises patients to read medicine leaflets carefully and consult healthcare professionals if they are unsure whether their medication increases sun sensitivity. 

Climate change and health concerns

According to the UK Met Office, a report from the Intergovernmental Panel on Climate Change (IPCC) concludes that human influence has warmed the atmosphere, oceans and land. 

The Met Office reports that average global land temperatures have already increased by more than 1°C since the Industrial Revolution, contributing to heatwaves that are becoming more frequent, longer-lasting and more intense.

The Met Office states that the UK's ten warmest years since 1884 have all occurred since 2002, while warm spells have more than doubled in average length compared with previous decades. 

Climate projections suggest hotter and drier summers will become increasingly common and by the end of the century temperatures of 40°C could occur every three to four years under a high-emissions scenario. 

The World Meteorological Organization (WMO), citing the IPCC Sixth Assessment Report, reports that human-caused climate change has increased the frequency and intensity of heatwaves since the 1950s and that additional warming will further increase these extremes. 

The WMO also notes that increasing temperatures and heatwaves have already contributed to higher rates of illness and death, with particularly severe impacts among vulnerable populations. 

Together, these findings highlight why medicine safety, hydration and heat-health awareness are becoming increasingly important public health issues in a warming climate.