A health warning has been issued for people taking five different types of medication, as they could experience dangerous side effects during the scorching temperatures of the current UK heatwave. A pharmacist has urged those on these drugs to take extra care as the mercury climbs this week, with Thursday tipped to be the hottest day of the year so far.
The blistering heatwave has created 'awful conditions' in hospitals, while schools and nurseries have closed or brought forward pick-up times or relaxed uniform rules, and train services have been thrown into chaos. South East Water has announced a temporary hosepipe ban for residents in Kent in response to 'high temperatures and record demand for water'. On Wednesday, the June temperature record – held since the notorious summer of 1976 – was shattered as provisional figures suggest it hit 36.1C in Gosport, Hampshire. The Met Office confirmed on Thursday that the UK record for the highest June minimum temperature has also provisionally been broken, with temperatures only dropping to 23.5C overnight at Bute Park, Cardiff.
How medications interfere with body temperature regulation
Dipa Kamdar, Senior Lecturer in Pharmacy Practice at Kingston University, outlined on The Conversation website that: 'The body uses several mechanisms to regulate temperature: sweating, blood flow to the skin and fluid balance. But some commonly prescribed drugs interfere with these processes, making it harder to stay cool.' She examined a range of medications routinely prescribed across the UK, stressing the importance of extra caution.
Antidepressants
Ms Kamdar highlighted that two particular types of antidepressants – selective serotonin reuptake inhibitors (SSRIs) and tricyclics (TCAs) – 'may make summer harder to cope with'. She said: 'They could even cause heat intolerance due to how they affect the body's ability to sweat.' Both these antidepressants are believed to function partly by affecting neurotransmitter levels in the brain – primarily serotonin and noradrenaline. This can lead to some patients sweating less, which during scorching weather, could make it more difficult for the body to regulate its temperature. Ms Kamdar said: 'Since sweating is a key cooling mechanism, any disruptions to this process can lead to heat-related illness. Excess sweating may also cause dehydration if fluids aren't replaced.'
Antipsychotics
Ms Kamdar explained: 'Antipsychotics are used to treat psychosis, which can occur in schizophrenia and bipolar disorder. They do this by blocking the neurotransmitter dopamine – which in turn affects levels of the neurotransmitter serotonin. This can disrupt the hypothalamus's ability to sense and respond to body temperature changes.' As a consequence, someone taking an antipsychotic might not feel overheated or thirsty when it's warm outside. This can result in low blood pressure and diminished heart function. 'The body then attempts to compensate by constricting the blood vessels and retaining heat. This consequently reduces perspiration and makes it more challenging to cool down effectively.'
Heart medications
Beta-blockers slow the heart rate and reduce the force at which the heart pumps blood. However, Ms Kamdar cautioned that this can limit blood flow to the skin – making it significantly harder for the body to release heat during warmer spells. She went on: 'Diuretics are also commonly used in the treatment of high blood pressure or heart failure. But as these drugs increase urine output, this may lead to dehydration and electrolyte imbalances during hot weather.' With less fluid available, the body may struggle to sweat properly. 'If you become severely dehydrated, you might actually stop feeling thirsty. Blood pressure can also drop, which may cause dizziness or fainting – especially when standing up.' She also pointed out that ramipril and losartan, similarly prescribed for blood pressure control, can increase the risk of dehydration. 'These drugs block a system in the body that helps control blood pressure, fluid balance and thirst. This may reduce your natural urge to drink, increasing dehydration risk when it's hot.'
Stimulants
Like amphetamines prescribed for ADHD, these substances impact multiple brain chemicals, including dopamine and noradrenaline. These effects can raise body temperature, accelerate metabolism and disrupt the body's ability to perspire, making it significantly harder to cool down, especially during physical activity or in warm weather. This could lead to dehydration, overheating, or even heatstroke. Stimulants may also disguise feelings of tiredness, prompting people to overexert themselves without recognising the potential danger to their health.
Insulin
Ms Kamdar outlined: 'Warm temperatures cause the body's blood vessels to dilate (widen) to aid in cooling off. However, this process results in faster absorption of insulin into the bloodstream due to increased blood flow to the area where insulin is injected – causing blood sugar levels to drop more rapidly.' This can result in hypoglycaemia (low blood glucose level), potentially causing symptoms such as dizziness, shaking, sweating, irritability, and even loss of consciousness or seizures. 'Heat can also degrade insulin, reducing its effectiveness and making it unsafe. This is why insulin should be stored in the fridge until use – especially in summer. Damaged insulin will change appearance – turning cloudy or changing colour.'
Preventative measures
To avoid heatstroke, Ms Kamdar suggests several preventative measures for those on common prescription drugs: Always check labels for storage instructions. Avoid leaving medications in hot places, such as in cars or on windowsills. Insulin isn't the only drug affected by heat – inhalers and EpiPens can also malfunction or become less effective. Stay hydrated when it's hot – unless your doctor has advised otherwise. Dehydration can actually worsen the effects of many medicines. For example, anti-inflammatory painkillers (such as ibuprofen) are more likely to cause kidney problems and bipolar medicines (including lithium) can become toxic if you're dehydrated. Avoid peak heat hours and stay in cool environments when possible. Watch for warning signs of heat-related illness – such as dizziness, confusion, nausea or excessive sweating. Don't stop taking your prescribed medication without medical advice. If it's affecting your ability to cope with the heat, speak with your doctor or pharmacist.
