MHRA warns some medicines can raise sun and heat risk

Hot weather advice usually begins with water bottles and sunscreen, but the MHRA wants you to think about something else as well: the medicines you take. In its Summer-proof your health campaign, the UK regulator says some prescription and over-the-counter treatments can make it harder for your body to cope with heat, stay hydrated or deal with strong sun. That does not mean every medicine becomes a summer problem. It does mean the weather can change the risks around medicines you may use every day, which is why the MHRA is asking people to check before a hot spell catches them out.

The MHRA says the main risks fall into three broad groups. Some medicines increase fluid loss, some affect the body's temperature control, and some make skin more sensitive to sunlight. When we put those together, the result can be dehydration, heat stress or faster, more severe burning than you might expect. Its examples are very familiar ones. Diuretics, often used for blood pressure or heart conditions, can make dehydration more likely. Some antidepressants and antipsychotics can affect temperature regulation, while beta blockers may reduce the body's response to heat stress.

Sun sensitivity is the part many people do not automatically connect with medication. The MHRA names antibiotics such as doxycycline and tetracycline, acne treatments including isotretinoin and topical retinoids, and the antifungal medicine voriconazole as treatments that can make skin react more strongly to sunlight. It also includes disease-modifying antirheumatic drugs, or DMARDs, such as methotrexate and azathioprine, which are used for conditions including rheumatoid arthritis, psoriatic arthritis and lupus. Proton pump inhibitors used for reflux and heartburn have also been linked to a very low risk of a lupus-like skin reaction triggered by sun exposure, and common painkillers such as ibuprofen and naproxen may increase sun sensitivity too.

**What this means for you:** common medicines are not automatically harmless in high temperatures or bright sun. The MHRA's advice is practical: keep up your fluids, avoid the strongest sun in the middle of the day where you can, and use protective clothing plus sunscreen if you are outdoors. It is just as useful to know the warning signs. The regulator says dizziness, headaches, unusual tiredness, confusion or passing less urine can all be clues that your body is struggling in the heat. Skin that turns red, sore, blistered or reacts more intensely after sun exposure can also point to medicine-related sensitivity.

Your first check should be the patient information leaflet that comes with your medicine. According to the MHRA, it should tell you whether to take extra care with sun exposure or hydration, and the same leaflet can also be found through the agency's online medicines directory if the paper copy has gone missing. The advice not to ignore is this: do not stop a prescribed medicine just because the weather is hot. If you are unsure how heat or sunlight might affect your treatment, the MHRA says the right next step is to ask a pharmacist or GP rather than make a change on your own.

There is also a reason the MHRA keeps asking people to report side effects. When patients flag problems, regulators can spot patterns and improve safety advice for everyone. If you think a medicine is causing a side effect, the agency says you can speak to a doctor, pharmacist or nurse, or report it directly through the Yellow Card scheme, which now allows sign-in using NHS login. For readers, this is a useful reminder about how to read health warnings. The story is not that summer is dangerous if you take medicines. The story is that some medicines change how your body handles heat and sunlight, and that a quick check now can make ordinary summer plans much safer.