MHRA warns medicines can raise heat and sun risks
If you take regular medication, summer heat is not just about feeling uncomfortable. In seasonal advice, the Medicines and Healthcare products Regulatory Agency, or MHRA, says some prescription and over-the-counter treatments can make it harder for your body to stay hydrated, keep cool or cope with strong sun. That is the thinking behind the agency’s Summer-proof your health campaign. The public message is simple, but important: a hot day can affect you differently when a medicine changes how your body handles fluid loss, temperature or sunlight.
The MHRA’s warning starts with heat. Diuretics, often used for blood pressure or heart conditions, can increase fluid loss and make dehydration more likely. Some antidepressants and antipsychotics can affect the body’s temperature control, while beta blockers may reduce how well the body responds to heat stress. **What this means for you:** the first signs may not feel dramatic. You might notice that you are more tired, more light-headed or less able to cool down than usual. That is exactly why warm-weather advice around medicines is worth taking seriously before symptoms build.
Sunlight is the other part of the picture. The MHRA says some medicines can make skin more sensitive to UV exposure, which means you may burn faster or more severely than expected. The examples it gives include antibiotics such as doxycycline and tetracycline, acne treatments such as isotretinoin and topical retinoids, and the antifungal medicine voriconazole. It also points to disease-modifying antirheumatic drugs, or DMARDs, including methotrexate and azathioprine, which are used for conditions such as rheumatoid arthritis, psoriatic arthritis and lupus. Proton pump inhibitors for reflux and heartburn have been linked to a very low risk of a lupus-like skin reaction triggered by sun exposure, and common painkillers including ibuprofen and naproxen may also increase sun sensitivity.
The symptoms to watch for are fairly clear, which helps. The MHRA says dizziness, headaches, unusual tiredness, confusion and reduced urination can all suggest your body is struggling in the heat. Skin that turns red, sore or blistered, or reacts much more strongly than expected after time in the sun, can also be a clue that a medicine is playing a part. **Why this matters:** these signs are easy to brush off as just the weather. But medicine safety often depends on noticing small changes early. If something feels off, it is worth stopping and asking whether heat, sun and medication could be interacting.
The practical advice is straightforward and manageable. Start with the patient information leaflet that comes with your medicine. The MHRA says it often includes guidance on sun exposure, hydration and side effects, and the same information can also be checked online through its medicines information service. From there, the small protective steps matter. Drink enough water, avoid the strongest sunshine in the middle of the day where you can, and use sun cream and protective clothing if you are outdoors. None of that replaces medical advice, but together these habits can reduce risk.
One point in the MHRA advice deserves to be said plainly: do not stop taking a prescribed medicine just because the weather turns hot. Many of these treatments manage long-term conditions, and stopping suddenly without advice can create a different health problem altogether. If you are unsure how your medicine might be affected by heat or sunlight, the safest next step is to ask a pharmacist or your GP. That is not overreacting; it is sensible medicine use. You do not need to guess when a trained professional can help you read the situation properly.
The MHRA also reminds people to speak to a doctor, pharmacist or nurse if they think they may be having a side effect. There is also the Yellow Card scheme, which lets patients report suspected side effects directly and helps regulators build a clearer picture of medicine safety. The agency notes that people can now use NHS login to create or access a Yellow Card account. Taken together, the message is calm rather than alarming. Summer does not mean your medicine is suddenly unsafe. It does mean a little extra care can go a long way, especially if hot weather, dehydration or strong sun are likely to be part of your day.