The UK government has issued essential advice for millions of people taking commonly prescribed medications, including ACE inhibitors like ramipril and beta-blockers like bisoprolol, as temperatures are forecast to exceed 30°C and reach up to 34°C across parts of the UK by Wednesday and Thursday this week.
The Medicines and Healthcare products Regulatory Agency (MHRA) published guidance on 26 June urging caution for patients on these and other drugs during extreme heat. Alison Cave, chief safety officer at the MHRA, stated: "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. 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."
Why heat affects medicines
The MHRA explains that most medications require storage below 25°C. During the recent heatwave, which peaked at a record 37.7°C and led to school closures, many homes, workplaces, and schools exceeded this temperature. Heat "breaks down the active ingredients in medicines," the agency warns, and medicines requiring refrigeration "are especially vulnerable." Affected medicines may no longer function correctly.
How medicines affect heat tolerance
While the body loses water through perspiration in warm weather, some medications can impair this process. The MHRA highlights that "blood pressure medicines such as ACE inhibitors, beta-blockers, or calcium channel blockers can also make it harder for your body to regulate temperature, especially during sudden hot spells. ACE inhibitors can even suppress your natural thirst response." Commonly prescribed ACE inhibitors include ramipril, captopril, and enalapril; widely used beta-blockers include atenolol, bisoprolol, and propranolol.
The agency also warns about other medications: "Some diabetes medicines, including insulin and metformin, also increase the risk of dehydration or make early symptoms harder to spot." Antipsychotics like olanzapine or quetiapine, and stimulants for attention disorders, can raise body temperature. Diuretics, such as furosemide, increase fluid loss through urination. Additionally, certain antibiotics, diuretics, antidepressants, or skin treatments for acne or eczema can increase sunburn susceptibility.
Signs of dehydration and safety tips
Dehydration symptoms include dizziness, headaches, fatigue, confusion, and dark urine, posing particular risks to elderly people, young children, and those with heart or kidney conditions. If feeling unwell in the heat, move to a cooler location, drink water gradually, and seek medical attention if condition fails to improve.
The MHRA advises: store medicines in a cool, dry place out of direct sunlight; avoid leaving them in cars or bags in sunlight; know the signs of heat-related illness; stay hydrated; take extra care in the sun if your medicine increases burn risk; and read the leaflet or consult a healthcare professional with any questions.
