As the UK experiences periods of rising temperatures, healthcare professionals are being reminded that hot weather can affect both the storage and effectiveness of medicines, as well as how patients respond to treatment.
The Medicines and Healthcare products Regulatory Agency (MHRA) has highlighted that exposure to heat may reduce the stability of certain medicines and increase the risk of adverse effects in vulnerable patients, particularly those with long-term conditions.
Alison Cave, Chief Safety Officer at the MHRA, said:
“During heatwaves, medicines are often unintentionally exposed to high temperatures in cars, bags, or sunny windowsills, which may affect how well they work when needed.
“Some medicines can also increase the risk of sun sensitivity, dizziness, or dehydration, particularly diuretics and treatments used in conditions such as asthma, cardiovascular disease, and diabetes.
“Patients should store medicines in a cool, dry place out of direct sunlight, stay alert to heat-related illness, and always refer to the patient information leaflet or a healthcare professional if unsure.”
Clinical considerations in hot weather
Most medicines are intended to be stored below 25°C, yet ambient temperatures in vehicles, transport, and sun-exposed environments can exceed this threshold quickly during heatwaves.
Heat exposure can lead to degradation of active ingredients, reducing therapeutic efficacy or altering pharmacokinetics. This is particularly relevant for temperature-sensitive medicines, including:
- Insulin and other injectable therapies
- Inhaled medications
- Hormone patches
- Adrenaline auto-injectors (eg. EpiPens)
- Certain liquid antibiotic formulations
Medicines requiring refrigeration are especially vulnerable if left outside recommended storage conditions, even for short periods.
Changes in colour, consistency, smell, or appearance may indicate heat damage. Such products should not be used, and pharmacist advice should be sought.
It is also important to recognise that heat itself can alter physiological responses to medication, including hydration status, blood pressure regulation, and drug absorption. This may affect patients with chronic conditions, particularly cardiovascular disease, diabetes, and respiratory illness.
Medical devices and heat exposure
Medical devices are also susceptible to environmental heat and humidity. For example, glucose monitoring systems and test strips may provide inaccurate readings if stored or used outside recommended conditions.
Patients should ensure devices are stored according to manufacturer guidance and kept in a cool, dry environment. Any unexpected readings or device performance issues should prompt a review and, where appropriate, clinical or pharmacy advice.
Key message for patients
During heatwaves, both medicines and medical devices require additional care. Patients should be encouraged to check storage instructions, avoid heat exposure, and seek professional advice if there is any concern about product stability or effectiveness.
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