The UK government has issued a warning that hot weather can compromise the effectiveness of a wide range of popular medications, including the contraceptive pill, inhalers, insulin, and EpiPens. The Medicines and Healthcare products Regulatory Agency (MHRA) reminded the public that high temperatures can alter how the body absorbs drugs and can degrade the active ingredients in medicines, rendering them less effective or ineffective.
Millions at Risk
According to the MHRA, up to 70% of the UK population receives a prescription for medication, meaning millions of people need to be aware of the risks. The agency's statement on the gov.uk website emphasises that most medicines should be stored below 25°C. Cars, trains, buses, and rooms with direct sunlight can quickly exceed this temperature, as can bags and pockets during a day out at a festival, sports event, or beach.
Contraceptive Pill in Focus
One particularly common medication affected is the contraceptive pill. Around 76% of women of reproductive age in the UK use some form of contraception, with over 3 million taking a contraceptive pill. Jason Murphy, head of pharmacy at online pharmacy Chemist4U, explained that the combined pill, mini pill, patch, and vaginal ring all contain hormones sensitive to temperature. 'Most are designed to be stored below 25°C, and prolonged exposure above 30°C can start to break down the hormones and reduce how well they work,' he said. 'A pill packet that’s spent a few days in a hot car, a handbag or beach bag, a steamy bathroom cabinet, or a windowsill isn’t necessarily going to protect you the way you’d expect – there’s a very real risk of unintended pregnancy as a result.'
Storage Guidelines
The MHRA advises reading patient information leaflets and storing medicines in the coolest part of the home, or in the fridge for heat-sensitive items like insulin or certain antibiotics. When travelling, avoid leaving medication in a vehicle and use a cool bag. The agency also warns that medical devices such as blood glucose monitors can give less reliable readings in hot or humid conditions. Test strips and devices should be kept in a cool, dry place, and users should check instructions for temperature guidance.
Signs of Compromised Medication
Murphy recommends checking for discoloured, sticky, or unusually soft pills as signs of heat damage. If a packet has been stored in a hot environment, he advises treating it as compromised and starting a new packet. He also suggests using a backup method of protection, such as condoms, for at least seven days. 'While it’s important that you don’t stop taking any prescription medications due to the heat, make sure you’re aware of how they might react to the weather,' he added. 'If something doesn’t feel right, make sure you speak to your pharmacist or GP.'
