26/05/2026
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⚠ A health warning has been issued for people taking certain types of medications, cautioning of possible harmful reactions in the rising heat.
🌡 A pharmacist has advised those on these medicines to take extra care as temperatures are expected to hit 35C today.
☀ The UK faces more records being broken today after the country experienced its hottest May day of all time. The nation also recorded its provisional all-time hottest meteorological spring temperature when Kew Gardens in south-west London hit 34.8C.
The expected high for large swathes of southern England and Wales on Tuesday is 35C – which could creep up to 36C, senior Met Office meteorologist Becky Mitchell said. Those forecasts span the Midlands, the south-east and south-west England, East Anglia, and South Wales.
Thunderstorms may be sparked in the afternoon, which will affect how hot it gets. Dipa Kamdar, Senior Lecturer in Pharmacy Practice at Kingston University, wrote 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 medicines widely prescribed across the UK, stressing the requirement for additional watchfulness.
Antidepressants
Ms Kamdar identified two particular types of antidepressants – selective serotonin reuptake inhibitors (SSRIs) and tricyclics (TCAs) – as potentially making summer more difficult to bear. These could include sertraline, fluoxetine (Prozac), citalopram in terms of SSRIs and for TCSs, smitriptyline, nortriptyline, and lofepramine
She explained: "They could even cause heat intolerance due to how they affect the body's ability to sweat." These antidepressants are believed to work partly by affecting neurotransmitter levels in the brain, chiefly serotonin and noradrenaline. This might result in some patients sweating less, which on a scorching day, could make cooling down difficult.
TCAs also increase noradrenaline levels, a neurotransmitter that stimulates sweat glands. This can increase sweating. In fact, both SSRIs and TCAs can increase sweating in users. Data shows up to 14% of antidepressant users experience this side-effect.
SSRIs may also interfere with the hypothalamus, the brain region that controls body temperature and tells the sweat glands to start producing sweat. But this signal may be affected by the increased serotonin levels.
Ms Kamdar clarified: "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 detailed: "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 changes in body temperature.
"As a result, 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 reduce heart rate and lower the force of heart pumping. However, Ms Kamdar noted that this can limit blood flow to the skin, making it harder for the body to release heat on hot days. She went on to say: "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."
Blood pressure medicines such as Ramipril and Losartan can also increase the risk of dehydration, she pointed out. "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
Prescribed amphetamines for ADHD, for example, affect several brain chemicals, including dopamine and noradrenaline. These effects can raise body temperature, accelerate metabolism, and disrupt the body's sweating mechanism, making it harder to cool down, particularly during physical activity or in hot weather.
This could potentially lead to dehydration, overheating, or even heatstroke. Stimulants may also suppress feelings of tiredness, causing people to push themselves too hard without realising the risk.
Insulin Ms Kamdar explained: "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.
This could potentially lead to dehydration, overheating, or even heatstroke. Stimulants may also suppress feelings of tiredness, causing people to push themselves too hard without realising the risk.
"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."
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 prescriptions medication without medical advice. If it's affecting your ability to cope with the heat, speak with your doctor or pharmacist.
✍ Ben Hurst
