People taking prescription or over-the-counter medicines are being urged to take extra precautions during hot weather, as some widely used treatments can increase the risk of
dehydration, heat-related illness or serious reactions to sunlight.
The warning has been issued by the Medicines and Healthcare products Regulatory Agency (MHRA) as part of its “Summer-proof your health” campaign, which aims to remind patients that medicines can affect the way the body responds to heat and sun.
According to the regulator, some medicines can interfere with the body’s ability to retain fluids or regulate its temperature, while others can make the skin significantly more sensitive to ultraviolet radiation.
Dr Alison Cave, the MHRA’s Chief Safety Officer, said the risks could be overlooked because many of the medicines involved are routinely prescribed or available without a prescription.
Diuretics, for example, are commonly used to treat high blood pressure and heart conditions but can increase fluid loss, potentially making dehydration more likely during hot weather. Some antidepressants and antipsychotics can interfere with temperature regulation, while beta blockers may reduce the body’s ability to respond to heat stress.
Other medicines can make the skin more vulnerable to sunlight. These include antibiotics such as doxycycline and tetracycline, acne treatments including isotretinoin and topical retinoids, and antifungal medicines such as voriconazole.
Some disease-modifying antirheumatic drugs (DMARDs), including methotrexate and azathioprine, can also increase sensitivity to sunlight. These medicines are frequently used to treat conditions such as rheumatoid arthritis, psoriatic arthritis and lupus.
The MHRA also highlights a small but recognised risk associated with proton pump inhibitors (PPIs), which are widely used for acid reflux and heartburn. These medicines have been linked to a very low risk of a lupus-like skin reaction triggered by sunlight.
Common painkillers should not necessarily be overlooked either. Non-steroidal anti-inflammatory drugs such as ibuprofen and naproxen can also increase sensitivity to sunlight in some people.
The regulator says patients do not need to stop taking their medicines simply because temperatures are rising. Instead, they should take sensible precautions and check whether their particular treatment carries additional risks.
People are advised to read the patient information leaflet supplied with their medicine, paying particular attention to warnings about sun exposure, dehydration and heat. Information for medicines is also available through the MHRA’s online product information service.
Signs that the body may be struggling in hot conditions include dizziness, headaches, unusual tiredness, confusion and passing urine less frequently than normal.
Skin reactions can also provide an important warning. Unusually intense redness, soreness or blistering after exposure to sunlight may indicate increased sensitivity caused by a medicine.
The MHRA recommends avoiding the strongest sunlight around the middle of the day where possible, wearing protective clothing and using sunscreen. Staying adequately hydrated is also particularly important for people taking medicines that can increase fluid loss.
Crucially, patients are being advised not to stop prescribed medicines without medical advice, even during periods of extreme heat.
Anyone uncertain about how their medication could interact with heat or sunlight should speak to a pharmacist or GP.
People who believe they are experiencing a side effect can also report it through the MHRA’s Yellow Card scheme. Reports help regulators identify previously unrecognised safety concerns and monitor the risks associated with medicines already in widespread use.
The MHRA says that a few simple precautions can help people continue taking their medicines safely while enjoying the summer.
