Heat can alter the potency of vital medicines and cause dangerous side effects, MHRA warns the public
Millions of Britons with diabetes, asthma, or high blood pressure have been warned to check how they store their medications as the UK braces for another sweltering weekend.
The Medicines and Healthcare products Regulatory Agency (MHRA) has issued fresh guidance, cautioning that extreme heat can degrade the effectiveness of widely used prescriptions — and even trigger dangerous side effects in some users.
As temperatures soar across England and Scotland, people are being urged to store medicines in cool, dry conditions away from direct sunlight. Leaving vital treatments like insulin, inhalers, hormone patches or EpiPens in hot environments — such as parked cars or window sills — can render them useless, or worse, dangerous.
Dr Alison Cave, MHRA’s chief safety officer, said:
“Let’s face it – when there’s a heatwave, most of us are focused on enjoying it. But it’s easy to forget that medicines left in the heat might not work properly when you need them. Some medicines can also make you more likely to burn, feel dizzy, or get dehydrated.”
According to the MHRA, medications that appear discoloured, have an unusual smell or altered texture may have suffered heat damage and should be checked by a pharmacist before further use.
The heat not only affects the medicines themselves — it can also amplify side effects or interfere with how the body reacts to certain treatments.
Dr Cave pointed to several high-risk categories:
- People with diabetes may struggle to manage blood sugar levels in the heat, particularly those taking insulin or metformin, which increase the risk of dehydration or mask early signs of heat exhaustion.
- Those on diuretics (or “water tablets” like furosemide) lose extra fluid through urination, and when combined with sweat loss in high temperatures, face a serious risk of mineral imbalance and dehydration.
- Blood pressure medications such as ACE inhibitors, beta-blockers, or calcium channel blockers can limit the body’s ability to regulate temperature, heightening vulnerability during heatwaves.
- Asthma sufferers, especially children and the elderly, must be particularly careful not to expose inhalers to high temperatures, which can alter dosage release or damage the medication’s effectiveness.
The MHRA’s warning follows multiple extreme heat alerts issued across the UK, including amber warnings for the South and temperature spikes expected in Scotland.
Dr Cave recommended three key steps for safe medication use in hot weather:
- Store medicines properly: Most should be kept under 25°C, some in fridges. Always follow label instructions.
- Stay alert to symptoms: Dizziness, headaches, fatigue and nausea can signal heat-related issues, especially in those taking medications.
- Stay hydrated: The heat and certain medications both deplete body fluids. Drink water regularly and avoid alcohol or excessive caffeine.
Pharmacists across the country have echoed the advice, urging patients not to wait until symptoms arise to act. “If in doubt, speak to your local pharmacist — don’t guess,” said one Glasgow chemist. “Heat can compromise a medication in hours.”
The alert comes amid rising concerns about climate change’s impact on public health and the fragility of everyday treatments under unseasonably hot conditions.
As the mercury climbs, those most vulnerable to chronic illnesses are once again being asked to take simple but life-saving precautions — and not let the sun cloud their judgment.
