The UK is experiencing another heatwave, and experts are warning that high temperatures can affect how well certain medications work, including the contraceptive pill. The Medicines and Healthcare products Regulatory Agency (MHRA) has issued a statement reminding people that heat can change how the body absorbs medication and can cause the medicine itself to stop working properly.
How heat affects medications
Most medicines need to be stored below 25°C, but cars, trains, and buses can heat up quickly in summer, and rooms with direct sunlight can become much hotter. Even bags and pockets can reach temperatures that cause problems, especially if you're out all day or at a festival, sports event, or beach. Heat can break down the active ingredients in medicines, making them less effective or ineffective when needed.
According to the MHRA, up to 70% of the population receives a prescription for medication, meaning millions of people need to be aware of this risk.
Contraceptive pill and heat
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. 'So, 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.'
Around 76% of women of reproductive age in the UK use some form of contraception, and more than 3 million are thought to be taking a contraceptive pill.
Storage tips and safety advice
To minimise risk, keep medicines in the coolest part of your home, or in the fridge if they are especially vulnerable to heat, such as insulin or certain antibiotics. When travelling, avoid leaving medication in a vehicle and use a cool bag. Check the patient information leaflet for storage instructions.
If pills become discoloured, sticky, or softer than usual, treat them as compromised and start a new packet. Jason Murphy also advises 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.'
Medical devices also affected
The MHRA notes that some medical devices, like blood glucose monitors, can provide less reliable readings if used or stored in hot or humid conditions. Keep devices and test strips in a cool, dry place and check instructions for temperature guidance. If a device isn't behaving as expected, run a control check or speak to a pharmacist.
