LONDON – Millions of Britons taking common antidepressants have been warned to take extra precautions this Bank Holiday weekend as the country braces for a possible record-breaking late-May heatwave, with temperatures forecast to climb toward 33C and health officials cautioning that several widely prescribed medications can quietly undermine the body’s ability to cope with extreme heat.
The UK Health Security Agency has issued amber heat health alerts for four regions of England and yellow alerts for the South West and northern England, warning vulnerable people that high temperatures over the coming days could place them at significantly greater risk. The Met Office has said the May UK temperature record of 32.8C is likely to fall over the weekend, with the mercury expected to peak on Monday across southern England and the Midlands.
For the roughly 8.6 million adults in England prescribed antidepressants each year, the alert carries a less visible warning. Common selective serotonin reuptake inhibitors, known as SSRIs, include sertraline, citalopram and fluoxetine, and they can interfere with the part of the brain that regulates body temperature. The same applies to serotonin-noradrenaline reuptake inhibitors, or SNRIs, such as venlafaxine and duloxetine, along with older tricyclic antidepressants and antipsychotic medications used to treat conditions including bipolar disorder and schizophrenia.
Dr Sameer Sanghvi, a GP and clinical technology lead at LloydsPharmacy Online Doctor, said the medications could blunt the body’s natural cooling defences. “Common antidepressants can all stop the temperature-regulating area of the brain from functioning as it should,” he said. “SNRIs are known to cause excessive sweating and dehydration, while SSRIs have been linked to heat intolerance and heat stroke.”
The hypothalamus, a small region deep inside the brain, acts as the body’s internal thermostat. It triggers sweating when core temperature rises, prompts thirst and signals blood vessels near the skin to widen, allowing heat to escape. Antidepressants that alter serotonin levels can dull that signalling system, leaving some patients sweating excessively while others sweat too little to cool down. Either response can lead to dangerous dehydration if temperatures remain high.
The amber alerts cover London, the East of England, the East Midlands and the South East, where forecasters expect the most intense heat. Dr Anya Gopfert, a consultant in health protection at UKHSA, said the warnings were not limited to the very elderly. “We know that even moderate heat can lead to serious health problems, especially for older people and those with certain health conditions, so it’s important that everyone takes simple precautions while enjoying the warm weather over the coming days,” she said.
The Met Office forecast points to highs of around 30C on Saturday, 32C on Sunday and a peak of 33C on Monday across southern England and the Midlands. Western Scotland and Northern Ireland are expected to be cloudier, with patchy showers, while coastal areas may see low cloud and sea fog. Deputy chief forecaster Steve Kocher said much of the UK would still enjoy dry, sunny weather even as the most extreme heat focused on the south.
Mental Health UK, which runs national support services, has highlighted the warning in its summer guidance, noting that temperature dysregulation is often listed as a side effect on medication leaflets but is rarely discussed at the point of prescribing. The charity has urged patients to read their leaflets carefully, drink plenty of fluids and speak to a pharmacist or GP if they feel unusually unwell in the heat, while stressing that no one should stop their medication abruptly.
The risk is not confined to antidepressants. Diuretics used for high blood pressure can accelerate fluid loss. Beta-blockers can reduce the heart’s ability to respond to heat stress. Some antihistamines can suppress sweating, and stimulant medications used to treat attention deficit hyperactivity disorder can raise body temperature. Doctors say the cumulative effect on patients taking multiple drugs is often underestimated, particularly among older people who may already be more vulnerable to dehydration.
Antidepressant use in England has risen sharply over the past decade, with NHS Business Services Authority data showing prescriptions up around 25 per cent compared with the period before the pandemic. The increase has been driven in part by rising rates of anxiety and depression among younger adults, as well as long-term prescribing in older patients. The wider patient base means even a small percentage at risk of heat-related complications translates into hundreds of thousands of people who may need to take additional care this weekend.
The UKHSA’s standard advice during heat health alerts is to stay out of direct sunlight between 11am and 3pm, drink water regularly, avoid alcohol and caffeine, keep curtains drawn in rooms facing the sun and check on elderly neighbours and relatives. Patients on psychiatric medication have been told to add a few extra steps, including carrying water at all times, avoiding strenuous exercise in the hottest part of the day and using high-factor sunscreen because some of the drugs also increase skin sensitivity to sunlight.
The heatwave arrives at a difficult moment for the NHS, which is already managing high seasonal demand and the fallout from a bitter dispute with resident doctors over pay and training posts. Emergency departments in southern England typically see a noticeable rise in heat-related admissions during prolonged hot spells, with older patients and those with chronic conditions most at risk of needing hospital care.
The latest warnings echo similar concerns raised during last summer’s prolonged heatwaves, when amber alerts covered all of England and emergency departments recorded their busiest June on record. They also land amid a wider international debate over psychiatric prescribing, with US health officials launching a sweeping review of antidepressant use earlier this month.
Dr Wendy Burn, a former president of the Royal College of Psychiatrists, said patients struggling with side effects should seek medical advice rather than stop taking their medication on their own. “Those struggling with the side effects should not come off their medication without consulting their doctor or specialist,” she said in earlier guidance that has been widely cited by NHS advisers this week.
For most patients, the practical message is straightforward. Stay cool, stay hydrated, stay informed about the symptoms of heat exhaustion, which include dizziness, nausea, muscle cramps, headaches and heavy sweating, and act quickly if they appear. Heat stroke, the more severe condition that can follow, is a medical emergency that requires an immediate 999 call. With temperatures forecast to remain elevated until at least Tuesday, doctors are urging the public to treat this Bank Holiday weekend less as a chance to bask in the sun than as a stress test for the body’s ability to cool itself, particularly for those whose medication may have already changed the rules.
