The UK government has issued a warning that hot weather can compromise the effectiveness of many popular medications, including the contraceptive pill, affecting millions of Britons. The Medicines and Healthcare products Regulatory Agency (MHRA) reminded the public that high temperatures can alter how the body absorbs drugs and can break down active ingredients, rendering them less effective or ineffective.
Millions at Risk
Up to 70% of the UK population receives at least one prescription medication annually, according to government data. This means millions could be affected by improper storage during heatwaves. The MHRA statement on gov.uk stresses that most medicines need to be stored below 25°C, but cars, trains, buses, and rooms with direct sunlight can quickly exceed that threshold.
Jason Murphy, head of pharmacy at online pharmacy Chemist4U, warned that the contraceptive pill is particularly vulnerable. 'Most are designed to be stored below 25C, and prolonged exposure above 30C 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.'
Which Medications Are Affected?
The warning covers a wide range of drugs, including tablets, inhalers, insulin, EpiPens, and more. Around 76% of women of reproductive age in the UK use some form of contraception, with over 3 million taking a contraceptive pill. The combined pill, mini pill, patch, and vaginal ring all contain heat-sensitive hormones. Other medications, such as antidepressants and weight-loss jabs like Ozempic and Mounjaro, have also been flagged as potentially less effective in heat.
Safe Storage Tips
The MHRA advises keeping medicines in the coolest part of the home, ideally in a fridge if specified (e.g., insulin, certain antibiotics). When travelling, avoid leaving medication in vehicles and use a cool bag. Always check the patient information leaflet for storage instructions. Murphy added that if pills appear discoloured, sticky, or softer than usual, they may be compromised. He recommends starting a new packet and using a backup contraceptive method, such as condoms, for at least seven days.
Medical Devices Also at Risk
The MHRA noted that blood glucose monitors and test strips can provide less reliable readings in hot or humid conditions. Devices should be kept in a cool, dry place, and users should follow temperature guidance. If a device behaves unexpectedly, a control check or pharmacist advice is recommended.
'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,' Murphy said. 'If something doesn’t feel right, make sure you speak to your pharmacist or GP.'
