ISLAMABAD: Some of the medicines most commonly prescribed for depression, anxiety, ADHD, high blood pressure and heart conditions can increase vulnerability to extreme heat, doctors and health organisations warn.
As climate change drives more frequent and intense heatwaves, medical experts are drawing greater attention to the interaction between high temperatures and medicines that can affect the body’s ability to cool itself.
The risk can be particularly significant for older people and those taking several medicines at the same time.
How medicines can affect the body’s response to heat
The human body normally responds to high temperatures by increasing sweating, widening blood vessels near the skin and reducing activity to prevent a dangerous rise in core temperature.
Some medicines can interfere with one or more of these mechanisms.
Psychiatric medicines, including several widely prescribed antidepressants, can affect the brain’s hypothalamus, which plays a central role in regulating body temperature.
Selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors (SNRIs) can increase sweating in some people. Excessive sweating during extreme heat can accelerate the loss of water and electrolytes, increasing the risk of dehydration.
Older antidepressants known as tricyclics can have the opposite effect. Their anticholinergic properties can reduce sweating, making it harder for the body to release heat.
Antipsychotic medicines can also interfere with the body’s normal temperature-regulation mechanisms and have been associated in studies with a greater risk of severe outcomes during heatwaves.
Stimulant medicines used to treat ADHD can increase heat production and constrict blood vessels. They may also reduce people’s awareness of physical exertion, potentially making it harder to recognise when the body is overheating.
Blood pressure and heart medicines
The risk is not limited to psychiatric medicines.
Diuretics, commonly prescribed for high blood pressure and heart conditions, increase the amount of water and salt eliminated from the body. During prolonged periods of extreme heat, this can contribute to dehydration and electrolyte imbalances.
ACE inhibitors and angiotensin receptor blockers, also widely used to treat high blood pressure, can affect the body’s fluid regulation and may increase vulnerability to dehydration in hot conditions.
Beta blockers can reduce blood flow to the skin, limiting the body’s ability to release heat.
Other medicines with anticholinergic effects, including some treatments for Parkinson’s disease, overactive bladder, respiratory conditions and allergies, can also interfere with sweating and cooling.
Multiple medicines can increase the risk
The risks may become more significant when people take several medicines that affect the body’s ability to regulate temperature or maintain adequate hydration.
Older adults are particularly vulnerable because the body’s ability to respond to heat generally becomes less effective with age, while people over 65 are also more likely to take multiple medicines.
Research has suggested that some older people taking combinations of diuretics, antipsychotics, beta blockers, stimulants and blood pressure medicines may face a higher risk of heat-related hospitalisation, even during periods that do not meet the definition of a heatwave.
However, doctors say more research is needed to establish which combinations carry the greatest risks.
Extreme heat can turn dehydration into a medical emergency
Heat-related dehydration can initially cause symptoms such as excessive thirst, weakness, dizziness, headache and fatigue.
If the body continues to overheat, more serious complications can develop, including kidney problems, cardiovascular stress and heatstroke.
Confusion, an altered mental state or unusual behaviour can be signs of severe heat illness and require urgent medical attention.
People taking medicines that may increase heat vulnerability are advised to take additional precautions during periods of extreme temperatures, including staying hydrated, avoiding direct sunlight during the hottest parts of the day and seeking cooler environments where possible.
Do not stop medicines without medical advice
Doctors stress that people should not stop taking prescribed medicines simply because of concerns about heat.
Instead, patients should discuss their medicines and individual heat-related risks with a doctor or pharmacist, particularly before periods of extreme weather.
Healthcare professionals are also being urged to consider heat vulnerability when prescribing medicines and to ensure that patients understand potential side effects and precautions.
As extreme heat becomes a more persistent feature of summer weather in many parts of the world, greater awareness of the relationship between medicines and temperature could help prevent avoidable illness and hospitalisation.
