Heatwave Warning: Common Medicines May Raise Risk of Dehydration

As heatwaves become more frequent and intense, doctors are warning that some widely used medicines may increase the risk of dehydration and other heat-related illnesses.

The concern covers several types of medication. These include some antidepressants, ADHD treatments, blood pressure medicines and heart drugs.

For some people, the combination of extreme temperatures and medication can make normal heat symptoms much worse. The medicines may affect sweating, thirst, blood flow or the body’s ability to regulate temperature.

Ileana Okumus, a 28-year-old living in Brussels, experienced this during Europe’s June heatwave. Her top-floor apartment reached 34C, leaving her struggling to cool down.

She eventually connected her symptoms with medicines she had started taking for depression and anxiety.

Doctors stress that people should not stop prescribed medication on their own. Some treatments carry significant risks if discontinued suddenly. Anyone concerned about heat-related side effects should speak with their doctor or pharmacist.

Antidepressants can affect heat regulation

Several medicines used to treat depression, anxiety and other mental health conditions can increase sensitivity to heat.

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Selective serotonin reuptake inhibitors, commonly known as SSRIs, include medicines such as sertraline, fluoxetine and escitalopram. Another group, serotonin and norepinephrine reuptake inhibitors, includes venlafaxine.

These medicines can influence the brain’s temperature-regulation system. Some people may also experience increased sweating.

Heavy sweating during extreme heat can lead to fluid and electrolyte loss. Dehydration can then make it harder for the body to cope with high temperatures.

Older tricyclic antidepressants can create a different problem. Some can reduce sweating because of their anticholinergic effects. That can prevent the body from releasing heat efficiently.

Caroline Fraissinet, a 36-year-old career coach in Los Angeles, noticed increased sweating and difficulty concentrating during a prolonged heatwave. She was taking an antidepressant, a mood stabiliser and ADHD medication.

The connection between her medicines and the heat was not immediately obvious.

ADHD and other psychiatric medicines

Stimulant medicines used to treat ADHD can also affect the body’s response to heat.

According to experts, these medicines can increase heat production and narrow blood vessels. They may also make people less aware of physical exertion, potentially allowing overheating to progress unnoticed.

Antipsychotic medicines can create additional concerns. Some affect the brain’s temperature-control mechanisms and have been associated with increased risks during previous heatwaves.

The risk can become more complicated when people take several medicines at the same time.

Doctors say the effects of different medicines can combine. Older adults may face particular risks because they are more likely to take multiple medications and are already more vulnerable to heat illness.

Blood pressure medicines can increase dehydration risk

Psychiatric medicines are not the only concern.

Some commonly prescribed medicines for high blood pressure and heart conditions can also affect how the body responds to extreme temperatures.

Diuretics increase the amount of fluid the body removes through urine. During a heatwave, this can contribute to dehydration and electrolyte problems.

ACE inhibitors and angiotensin receptor blockers can also influence the body’s fluid and blood-pressure regulation.

Beta blockers may reduce blood flow to the skin. This can make it harder for the body to release excess heat.

Other medicines with anticholinergic effects can interfere with sweating. Doctors say these include treatments used for several conditions, including allergies, respiratory problems and overactive bladder.

The combination of medicines can be particularly important. A person taking several drugs that affect hydration or cooling may face a greater risk than someone taking only one.

Heat risk is not the same for everyone

Medication is only one part of the picture.

Living without air conditioning, working outdoors or spending long periods in direct sunlight can increase exposure to extreme temperatures. People living in urban areas with limited green space may also face higher temperatures.

Older adults and people taking multiple medicines can face additional risks.

Emergency medicine physician assistant Cecilia Ahanonu described treating a man in his 60s during a Las Vegas community health event when temperatures reached about 43C.

The man was taking a diuretic and an SSRI. He was sweating heavily, had a fast heart rate and appeared pale.

Ahanonu advised him to increase fluid intake, avoid the hottest part of the day and use cooling facilities. She also warned him about signs that could indicate heat stroke.

Confusion, an altered mental state or unusual behaviour can signal a medical emergency. Anyone showing these symptoms during extreme heat needs urgent medical attention.

Doctors call for greater awareness

Medical experts say patients need clearer information about how their medicines may interact with extreme temperatures.

Doctors also need better training, particularly as climate change increases the frequency and severity of heatwaves.

For patients, the key message remains simple: do not stop prescribed medication without medical advice.

Instead, people who take regular medicines should ask their doctor or pharmacist whether their treatment can increase heat sensitivity. They can also discuss practical steps to stay hydrated and cool during periods of extreme heat.

Understanding the connection between medication and heat could help vulnerable people recognise warning signs earlier and avoid potentially serious complications.