The UK Health Security Agency (UKHSA) has issued a warning that the ongoing July heatwave could silently damage life-saving medications, including insulin, EpiPens, and asthma inhalers, potentially rendering them ineffective. The alert, shared on Wednesday, July 8, 2026, comes as the Met Office confirms Britain is experiencing its third heatwave of the year.
Heat Exposure Risks for Medications
Most medications are formulated to be stored below 25°C. However, regulators caution that cars, buses, and trains can become furnaces within minutes during heatwaves. Even a warm handbag or trouser pocket exposed to sunlight may compromise essential treatments. The Medicines and Healthcare products Regulatory Agency (MHRA) warns that insulin and certain liquid antibiotics requiring refrigeration are particularly vulnerable and may cease functioning if exposed to heat for extended periods.
Alison Cave, the MHRA's chief safety officer, stated that many people are so preoccupied with enjoying the sunshine that they overlook the danger. She acknowledged that medicines left baking in the heat 'might not work properly when you need them' and warned that some drugs can also make patients more susceptible to sunburn, dizziness, or dangerous dehydration.
Signs of Heat-Damaged Medication
Health officials warn that heat-damaged medication may not always appear different, but patients should look for changes in colour, smell, or texture, which can indicate a drug has been compromised. Blood glucose monitors used by diabetics can also be affected by heat and humidity, potentially giving unreliable readings.
Dehydration Risks for Specific Medications
The alert includes a caution for millions taking diuretics, or 'water tablets', such as furosemide, who are already losing extra fluid through sweat and urination, raising the risk of dehydration and dangerous mineral imbalances in extreme heat. Widely used blood pressure medications, including ACE inhibitors, beta-blockers, and calcium channel blockers, can make it harder for the body to regulate its temperature. ACE inhibitors in particular may suppress the body's natural thirst response, leaving patients unaware they need to increase fluid intake.
Those taking insulin or metformin for diabetes face a heightened dehydration risk, while patients on antipsychotic drugs such as olanzapine and quetiapine, or stimulant medication for attention disorders, may find their bodies struggle to cool down. Officials warn that dizziness, headaches, fatigue, confusion, and dark urine are telltale signs of dehydration, which is particularly hazardous for the elderly, young children, and those with heart or kidney conditions.
Sunburn Risk from Common Tablets
Patients have also been told that a range of everyday medications could leave their skin significantly more susceptible to sunburn, even on mildly sunny days. Certain antibiotics, diuretics, antidepressants, and acne or eczema treatments are among those highlighted, along with painkillers such as ibuprofen and naproxen, though officials stressed this risk is more commonly associated with frequent or long-term use.
Particular concern surrounds methotrexate, a drug used to treat rheumatoid arthritis, psoriasis, Crohn's disease, and cancer, which can trigger extreme sun sensitivity even at low doses. Officials warn this can result in painful blistering rashes resembling severe sunburn and, in rare cases, has led to serious infections. Even a brief dog walk, gardening, or a sunny commute could provoke a reaction in vulnerable patients.
The regulator advises anyone worried about their medication to check the patient information leaflet or consult their pharmacist, and to report suspected issues through the MHRA's Yellow Card scheme.
