MHRA Warns Some Medicines Raise Heat and Sun Risks

Summer health advice usually starts with drinking water and keeping out of strong sun. The MHRA says there is another check worth making too: the medicine in your bag, bathroom cabinet or daily pill box. In its Summer-proof your health campaign, the medicines regulator is reminding people that some prescription and shop-bought treatments can make it harder for the body to cope with hot weather. That does not mean the medicine is wrong for you. It means summer can change the risks around it, and you deserve to know how.

The MHRA's advice is built around three simple ideas. Some medicines can make you lose more fluid, which raises the chance of dehydration. Some can affect how well your body controls its temperature. Others can make your skin more sensitive to sunlight, so you may burn faster or more badly than you expect. **What this means for you:** a medicine does not have to be rare or unusual to matter here. The warning covers some very common treatments, including tablets people take every day for blood pressure, heart conditions, pain relief, acne, reflux and mental health.

One example is diuretics, which are often prescribed for high blood pressure or heart conditions. These medicines help the body get rid of extra fluid, but in hot weather that can also make dehydration more likely if you are not replacing what you lose. The MHRA also says some antidepressants and antipsychotics can affect temperature control, while beta blockers may reduce the body's response to heat stress. Put plainly, that can leave you feeling the heat more sharply, or make it harder for your body to cool itself in the usual way.

Sunlight can be part of the problem too. The MHRA lists certain antibiotics, including doxycycline and tetracycline, as medicines that can increase photosensitivity. Some acne treatments, such as isotretinoin and topical retinoids, can do the same, as can the antifungal medicine voriconazole. The warning also includes disease-modifying antirheumatic drugs, often called DMARDs, such as methotrexate and azathioprine. These are used for conditions including rheumatoid arthritis, psoriatic arthritis and lupus. The regulator adds that proton pump inhibitors, used for acid reflux and heartburn, have 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 also raise sun sensitivity.

This is the part many of us miss: the signs can look like ordinary summer discomfort until they become harder to ignore. The MHRA says warning signs include dizziness, headaches, unusual tiredness, confusion and passing less urine than usual. If your skin becomes red, sore, blistered or reacts more strongly than expected after time in the sun, that may also point to medicine-related sensitivity. A useful rule is not to brush off every symptom as 'just the weather'. If something feels different from your normal pattern, it is worth checking whether your medicine leaflet mentions heat, hydration or sun exposure.

The safest first step is simple. Read the patient information leaflet that comes with your medicine, because that is where specific advice on sunlight, hydration and storage is usually set out. The MHRA says people should also stay hydrated, avoid the strongest sun in the middle of the day where possible, and use protective clothing and sun cream. Just as important, do not stop taking prescribed medicine on your own because temperatures rise. If you are unsure how your treatment behaves in hot weather, the regulator's advice is to speak to a pharmacist or GP. That conversation matters more than guesswork, especially if the medicine is for a long-term condition.

There is a wider public-interest lesson in this warning. Medicines do not work in isolation from daily life. Heat, sunlight and dehydration can change how safe or comfortable treatment feels, even when you are taking it correctly. If you think you are having a side effect, the MHRA says you should speak to a doctor, pharmacist or nurse. You can also report suspected side effects through the Yellow Card scheme, which helps the regulator track problems and improve medicine safety for everyone. For readers, the takeaway is straightforward: before the next hot spell, check your leaflet, know your warning signs and ask for advice early rather than late.