Pharmacologist Warns of Heat-Damaged Medicines as UK Reaches 36C
Health officials are urging anyone taking medication during the UK heatwave to follow three critical steps to stay safe. The Medicines and Healthcare products Regulatory Agency (MHRA) has issued a reminder that hot conditions can affect medicines and how well they work, as temperatures could reach as high as 36C this week. An amber heat-health alert is in force across most of England, including Greater Manchester and the north west.
Pharmacologist Dr Alison Cave, the MHRA's chief safety officer, said: "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."
Step One: Check Where Medicines Are Stored
The MHRA advises that most medicines need to be stored at temperatures below 25C. During summer, cars, trains, buses, and rooms getting direct sunlight can become much hotter than expected. Even bags and pockets can get warm enough to cause problems, especially if you're out all day at a festival, sports event, or the beach.
Heat can break down the active ingredients in medicines, meaning they might not work when needed. This includes tablets, inhalers, hormone patches, insulin, and EpiPens. Some packaging gives clear storage instructions, but not all medicines come with a visible warning. Medicines that need to be kept in the fridge – such as insulin or certain liquid antibiotics – are particularly vulnerable. If left out too long, they may not work properly. If your medicine has changed colour, developed an unusual smell, changed texture, or looks different, this could signal heat damage. Ask your pharmacist for advice.
At home, check the patient information leaflet and keep medicines in the coolest part of the house, away from direct sunlight. When travelling, avoid leaving them in parked vehicles or warm bags. A cool bag can help if you're going to be out all day. Heat damage can also affect how much medicine your body absorbs, potentially making your usual dose too strong or too weak. If you notice changes in how you feel or how well your medicines work during hot weather, speak to your pharmacist or doctor.
The MHRA also urges people not to forget medical devices, as they can be affected by heat or humidity. For example, blood glucose monitors may give less reliable readings if used or stored in hot conditions. Keep devices and test strips somewhere cool and dry, and check the instructions for temperature guidance. If your device isn't behaving as expected, run a control check or speak to your pharmacist.
Step Two: Drink More Water and Stay Cool
During hot weather, the body loses more water through sweating, and some medicines can worsen this or make it harder for the body to cope with heat. People taking diuretics ("water tablets") such as furosemide are already losing more fluid through urination, which can cause dehydration and mineral imbalances. Blood pressure medicines like ACE inhibitors, beta-blockers, or calcium channel blockers can also make it harder for the body to regulate temperature, especially during sudden hot spells. ACE inhibitors can even suppress the natural thirst response.
Some diabetes medicines, including insulin and metformin, increase the risk of dehydration or make early symptoms harder to spot. Antipsychotic medications such as olanzapine or quetiapine, or stimulant medications for attention disorders, can increase body temperature, making overheating more likely. Dehydration can cause dizziness, headaches, tiredness, confusion, and dark urine. This is particularly dangerous for older adults, young children, and people with heart or kidney conditions. If you feel unwell in the heat, move somewhere cooler, sip water slowly, and seek medical advice if you don't improve quickly.
Step Three: Check Your Risk of Sunburn
Some common medicines can make the skin much more likely to burn, even in mild sunshine. This includes some antibiotics, diuretics, antidepressants, or skin treatments for acne or eczema. Painkillers such as ibuprofen or naproxen are also known to sometimes cause mild sun sensitivity, though this is less common and usually only a concern with frequent or long-term use.
One medicine requiring particular care is methotrexate, used to treat rheumatoid arthritis, psoriasis, Crohn's disease, and cancer. It can cause extreme skin sensitivity to the sun, even at low doses, leading to painful rashes, blistering, or swelling that looks like severe sunburn. In rare cases, these reactions have led to serious infections. The risk increases during sunny weather, especially if you're outside more – whether walking the dog, gardening, or on holiday. Even a short walk at lunchtime or a train ride in the sun can trigger a reaction for some people.
Dr Alison Cave added: "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."
