The Medicines and Healthcare products Regulatory Agency (MHRA) has re-issued its caution about protecting medicines during extreme heat, a warning that is again relevant as UK temperatures are expected to top 30C on Monday and stay in the mid-to-high 20Cs for the rest of the week. Millions of people who take common prescription drugs, including ACE inhibitors such as ramipril and beta-blockers such as bisoprolol, are affected.
On 26 June, the MHRA re-issued guidance on keeping medicines safe during hot weather, after the UK experienced a heatwave that peaked at a record 37.7C and led to school closures. With hot conditions returning, the agency's advice has become essential once more.
Alison Cave, chief safety officer at the MHRA, said: "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 your medication
The MHRA says most medicines need to be stored below 25C, a threshold frequently surpassed this summer in homes, cars, schools and workplaces. Heat breaks down the active ingredients in medicines, and those that require refrigeration are especially vulnerable. If a medicine is exposed to heat, it may stop working correctly.
How medicines affect the body's response to heat
In warm conditions, the body loses more water through sweat, but the MHRA warns that some medicines can make this effect worse or make it harder for the body to cope. The agency specifically highlights blood pressure drugs: "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."
Common ACE inhibitors prescribed in the UK include ramipril, captopril and enalapril. Widely used beta-blockers include atenolol, bisoprolol and propranolol.
NHS and British Heart Foundation guidance
The NHS notes that ramipril can cause dizziness, particularly when standing up quickly, and this risk increases in hot weather because of lower blood pressure and dehydration. The British Heart Foundation (BHF) also urges heart patients, many of whom take both ramipril and bisoprolol, to take extra care during hot spells. The BHF says people with heart conditions are at greater risk of heat-related illness because their cardiovascular systems are already under strain, and high temperatures place additional pressure on the heart. It recommends staying cool indoors during the hottest parts of the day, drinking plenty of fluids, and speaking to a GP or pharmacist if concerned about medication and heat.
Other medicines that need extra caution
The MHRA also warns that several other types of medication can increase the impact of hot weather. Some diabetes medicines, including insulin and metformin, raise the risk of dehydration or make early symptoms harder to spot. Antipsychotic drugs such as olanzapine or quetiapine, as well as stimulants for attention disorders, can increase body temperature and make overheating more likely. People taking diuretics, or "water tablets", such as furosemide, are already losing more fluid through urination.
Additionally, certain common medicines can increase sensitivity to sunburn, including some antibiotics, diuretics, antidepressants, and skin treatments for acne or eczema.
Dehydration signs and keeping medicines safe
Dehydration can lead to dizziness, headaches, fatigue, confusion and dark urine. It poses a particular risk to older people, young children, and those with heart or kidney conditions. If you start to feel unwell in the heat, move to a cooler place, drink water gradually, and seek medical attention if you do not improve quickly.
To keep medicines safe during hot weather, the MHRA advises:
- Store medicines in a cool, dry place out of direct sunlight.
- Do not leave them in cars or in bags left in the sun.
- 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 prone to burning.
- Read the leaflet or speak to a healthcare professional if you have questions.
