Why certain meds can make heatwaves harder to handle

Some of the most prescribed medications, including those used to treat depression, ADHD and high blood pressure, can increase the risk of dehydration and other heat-related conditions.

This year, at the height of Europe's June heatwave, Ileana Okumus couldn't understand why she was struggling so much more than other people.

"As soon as I left my apartment, my face started to sweat," she says. Living in a top-floor Brussels apartment without air conditioning, the 28-year-old sought relief wherever she could find it – the office, local cafes. But it wasn't enough.

"I had to wait half an hour, an hour, before I cooled down," she says. "There was one particular day when the temperature inside the apartment reached 34C [93F]. I think I slept around 18 hours." She found it difficult to wake up, and worried that her blood pressure might have dropped. 

The intensity of the heatwave was nothing new for Okumus, who has lived through 40C [104F] summers elsewhere in the world. Yet it was the first time the heat had hit her this hard. Only after seeing social media posts from people with similar symptoms did she make the connection between the heat and the medicines she'd started taking two years ago for depression and anxiety. 

As heatwaves become more frequent and severe as a result of climate change, doctors and health organisations are warning that some of the most commonly taken drugs – including psychiatric, blood pressure and heart medications – can interfere with the body's ability to regulate its temperature, and are putting people at risk of heat-related illness.

Mental health drugs in the heat

Many types of drugs used to treat mental health conditions, including depression, anxiety, and bipolar disorder, are known to increase heat vulnerability due to how they interact with the hypothalamus, the brain's thermoregulation centre.

"This area of the brain gets us to reduce our activity, to sweat more, to reduce our metabolism – all beneficial adaptations to heat," says Robert Feder, a retired psychiatrist based in New Hampshire and member of the steering committee for the Medical Society Consortium on Climate and Health.

That includes the most widely prescribed antidepressants, SSRIs (selective serotonin reuptake inhibitors) and SNRIs (serotonin and norepinephrine reuptake inhibitors). Drugs in these classes include sertraline, fluoxetine, escitalopram and venlafaxine. They function by blocking the brain's reuptake of serotonin, a naturally occurring chemical that regulates mood and other bodily functions.

Too much serotonin in the hypothalamus can disrupt thermoregulation and cause excessive sweating. This affects around one in five people taking antidepressants and can lead to dehydration and electrolyte loss. 

"That becomes a compounded problem when you're already dehydrated because of high temperatures," says Feder.

Tricyclic antidepressants, an older type of antidepressant, can also trigger sweating – or suppress it instead, also a problem since it reduces heat elimination and raises body temperature. These antidepressants have an "anticholinergic" effect, meaning they block activity of a neurotransmitter called acetylcholine, which is involved in many different bodily functions including sweat production.

The combined effects of taking three different psychiatric medications – an antidepressant, a mood stabiliser and ADHD medication – have taken a toll this summer on Caroline Fraissinet, a 36-year-old career coach in Los Angeles. In the middle of an unusually long, humid heatwave in July, she found herself losing focus, feeling more........

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