The Medicines and Healthcare products Regulatory Agency, MHRA, has issued fresh advice urging people to take extra care with medicines during the current spell of hot weather across the UK.
The agency warned that high temperatures can affect how medicines work and how the body responds to them, particularly for people managing long-term health conditions.
The warning comes as temperatures continue to rise across many parts of the country.
Alison Cave, Chief Safety Officer at the MHRA, said medicines left in hot conditions, including cars, bags, or sunny windowsills, may not work properly when needed.
She also warned that some medications can increase the risk of dehydration, dizziness, or sunburn during periods of extreme heat.
The MHRA is advising people to store medicines somewhere cool, dry, and away from direct sunlight, and to stay hydrated during hot weather.
According to the agency, most medicines should be stored below 25C. It warned that cars, buses, trains, and rooms exposed to direct sunlight can quickly exceed safe temperatures during summer conditions.
The guidance applies to a range of medicines including tablets, inhalers, insulin, hormone patches, and EpiPens.
Medicines that require refrigeration, such as insulin and some liquid antibiotics, are considered especially vulnerable to heat damage.
The MHRA said signs of heat damage can include medicines changing colour, texture, or smell. Patients are being advised to speak to a pharmacist if they notice any changes.
Medical devices may also be affected by heat and humidity. The agency said blood glucose monitors used by people with diabetes may give less reliable readings if stored or used in very warm conditions.
People taking diuretics, commonly known as water tablets, are also being urged to take extra care during hot weather because these medicines increase fluid loss through urination.
The MHRA said some blood pressure medicines, including ACE inhibitors, beta-blockers, and calcium channel blockers, can make it harder for the body to regulate temperature.
It also warned that some diabetes medicines, antipsychotic medications, and stimulant medications for attention disorders may increase the risk of overheating or dehydration.
Symptoms of dehydration can include dizziness, headaches, tiredness, confusion, and dark urine.
The advice also highlights the increased risk of sunburn linked to some medications. These include certain antibiotics, antidepressants, acne and eczema treatments, and some anti-inflammatory painkillers.
The MHRA said methotrexate, a medicine used to treat conditions including rheumatoid arthritis, psoriasis, Crohn’s disease, and some cancers, can cause severe sensitivity to sunlight, even at low doses.
The agency is advising patients to read the information leaflet supplied with their medicines and seek advice from a pharmacist or healthcare professional if they have concerns.
Three important tips from the MHRA:
1. Keep medicines out of hot cars and direct sunlight
Most medicines need to be stored at temperatures below 25°C. But cars, trains and buses can heat up quickly during the summer, and rooms with direct sunlight can get much hotter than you’d think. Even bags and pockets can get warm enough to cause problems, especially if you’re out all day or at a festival, sports event, or the beach.
Heat can break down the active ingredients in medicines, meaning they might not work when you need them. That includes tablets, inhalers, hormone patches, insulin, and EpiPens. Some packaging will give 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 especially vulnerable to heat. If they’re left out too long or stored incorrectly, they may not work properly when you take them.
If your medicine has changed colour, developed an unusual smell, changed texture, or looks different in any way, this could signal heat damage. Ask your pharmacist for advice.
If you’re at home, check the patient information leaflet for storage instructions and keep medicines in the coolest part of the house, away from direct sunlight. If you’re 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 any changes in how you feel or how well your medicines seem to be working during hot weather, speak to your pharmacist or doctor.
Don’t forget medical devices:
It’s not just medicines – some medical devices can also be affected by heat or humidity. For example, blood glucose monitors may give people managing diabetes less reliable readings if used or stored in hot conditions.
Keep devices and any test strips somewhere cool and dry, and check the instructions that came with them for any temperature guidance. If your device isn’t behaving as expected, try running a control check or speak to your pharmacist for advice.
For more information about medicine and medical device safety, visit the MHRA website or report any concerns through the MHRA’s Yellow Card scheme.
2. Drink more water and stay cool if you’re taking diuretics or blood pressure medication
During hot weather, your body loses more water through sweating – but some medicines can make this worse, or make it harder for your body to cope with heat.
People taking diuretics, or ‘water tablets’, such as furosemide, are already losing more fluid through urination. This can cause dehydration and mineral imbalances. 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.
Some diabetes medicines, including insulin and metformin, also 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 your body temperature, making you overheat more easily.
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 start to feel unwell in the heat, move somewhere cooler, sip water slowly, and seek medical advice if you don’t feel better quickly.
3. Check if your medicine increases your risk of sunburn
Some common medicines can make your 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, but this is less common and usually only a concern with frequent or long-term use.
One medicine that requires particular care is methotrexate, used to treat conditions like rheumatoid arthritis, psoriasis, Crohn’s disease and cancer. It can cause extreme skin sensitivity to the sun – even at low doses. This can lead to painful rashes, blistering, or swelling that looks like severe sunburn. In rare cases, these reactions have led to serious infections.
The risk goes up during sunny weather, especially if you’re outside more – whether you’re walking the dog, gardening, or heading off on holiday. Even a short walk at lunchtime or a train ride in the sun can be enough to trigger a reaction for some people.
If you take any medicines, always read the patient information leaflet or check with your pharmacist to see if sun sensitivity is a side effect.
- Worried about your health? Speak to your doctor, pharmacist or to call NHS 111 if you are worried about your health.
- Concerns about medicines or medical devices can also be reported through the MHRA’s Yellow Card scheme.
