As the UK continues to experience intense heatwaves, the Medicines and Healthcare products Regulatory Agency (MHRA) has issued an urgent alert for individuals on certain medications or with specific health conditions. Elevated temperatures, direct sunlight, and side effects from some medicines can all impact treatment safety and effectiveness.
Medicines and medical devices are often vulnerable to heat. Alison Cave, Chief Safety Officer at the MHRA, emphasizes: “Medicines exposed to excessive heat may not work properly when you need them. Some can increase your risk of sunburn, dizziness, or dehydration—especially if you are taking diuretics or have conditions like asthma, heart disease, or diabetes.”
Key precautions to stay safe include:
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- Store medicines at or below 25°C. Many tablets, inhalers, hormone patches, insulin, and emergency devices like EpiPens degrade when overheated, reducing their effectiveness or altering how your body absorbs them.
- Always check for visible warning labels and storage instructions on medication packaging.
- Inspect your medicines regularly. Changes in color, smell, texture, or appearance may indicate heat damage—consult your pharmacist without delay.
- Protect medical devices and test strips from humidity and sunlight as these can impair function. If a device malfunctions, perform a control check, ask your pharmacist for help, and report concerns via the MHRA Yellow Card Scheme.
Certain medications increase vulnerability to heat-related issues. Diuretics, often called “water tablets,” cause you to lose more fluids, raising dehydration and mineral imbalance risks. Blood pressure medications (including ACE inhibitors, beta-blockers, and calcium channel blockers), stimulant drugs, and antipsychotics may hamper your body’s temperature regulation or raise your baseline temperature, making overheating more likely.
For example, ACE inhibitors can suppress your natural thirst response, making it harder to stay hydrated during sudden heat spells.
Symptoms of dehydration include dizziness, headaches, fatigue, confusion, and dark urine. If you feel unwell in the heat, immediately move to a cooler location, sip fluids slowly, and seek medical advice if symptoms persist.
Moreover, some antibiotics, diuretics, antidepressants, painkillers, and topical treatments for acne or eczema increase skin sensitivity to sunlight—even mild sun exposure—heightening the risk of burns.
Individuals taking methotrexate must also take extra care, as this medication can cause severe photosensitivity. Even at low doses, methotrexate can lead to painful rashes, blistering, or swelling resembling severe sunburn, occasionally resulting in serious infections. Methotrexate is prescribed for conditions such as rheumatoid arthritis, psoriasis, Crohn’s disease, and certain cancers.
The MHRA advises always reading the medicine leaflet and consulting healthcare professionals with any concerns to ensure your treatments remain safe and effective during heatwaves.