The Medicines and Healthcare products Regulatory Agency (MHRA) published advice on 7 August 2026 warning that some prescription and over-the-counter medicines can make it harder for the body to stay hydrated, regulate temperature or cope with sun exposure. The guidance formed part of the agency's "Summer-proof your health" campaign.

Dr Alison Cave, the MHRA's Chief Safety Officer, said diuretics can increase fluid loss, some antidepressants and antipsychotics can affect temperature regulation, and beta blockers may reduce the body's response to heat stress. She listed certain antibiotics including doxycycline and tetracycline, acne treatments such as isotretinoin and topical retinoids, and the antifungal voriconazole as medicines that can increase sensitivity to sunlight. She also cited DMARDs such as methotrexate and azathioprine, a very low risk of a sun-triggered lupus-like skin reaction linked to proton pump inhibitors, and painkillers such as ibuprofen and naproxen.

The agency encouraged people to read the patient information leaflet, watch for signs such as dizziness, headaches, unusual fatigue, confusion or reduced urination, and avoid stopping prescribed medicines in hot weather without advice. It advised speaking to a pharmacist or GP with questions and reporting suspected side effects through the Yellow Card scheme.