Some medications and heat waves don't mix, experts say precautions needed

As Central and Eastern Canada brace for the year's first heat wave, medical experts are warning of the particular health risks faced by people taking medications that can alter the body's response to extreme temperatures.

Dr. Samantha Green, a family physician at Unity Health Toronto — a network comprised of three hospitals — said the increasing frequency of heat waves as the climate changes has brought the role of medications to the forefront.

People who are more at risk in extreme heat events include seniors, infants and toddlers, as well as those with chronic physical and mental health conditions. Sometimes those health conditions can impair thermal regulation, making it hard for people to cope with heat, Green said. Compounding the problem, certain drugs taken for those conditions can then further impede heat regulation, although experts stress that is not a reason to skip medications.

Blood pressure medications, for example, may cause dehydration, while antidepressants and antipsychotics can impair the hypothalamus — a gland in the brain that acts like a thermostat — and interfere with the body's ability to regulate heat, she said. For people taking multiple medications, Green said, "thermoregulation can be doubly or triply impaired."

Nasheena Poonja, a clinical pharmacist and lecturer at the University of British Columbia, said it's important to understand that older adults are at a greater risk during heat waves because the body's ability to regulate temperature decreases with age. Older bodies tend to retain more heat than younger ones, because they don't sweat as much, she added.

Their health risk is further compounded by any chronic conditions they may have and the medications prescribed for them, Poonja said. "Some of those medications may actually contribute to the body's heat intolerance or ability to regulate that heat."

Medications that may cause complications include those for heart-related problems such as beta blockers or ACE inhibitors, she said. And people who are prescribed diuretics can experience reduced thirst sensation, dehydration, electrolyte imbalances and fainting. Some antihistamines and anti-seizure medications can affect the body's ability to regulate temperature, which can also be dangerous in the heat, she noted. 

But Poonja said people can't stop taking medications just because there's a heat wave. Rather, they or their caregivers need to plan ahead by assessing the weather forecast and charting out how to stay cool and hydrated, even setting timers to remind them to drink water. There should be someone to check on older adults to ensure they aren't overheated.

"So you know, asking certain questions or just assessing them very briefly to make sure that the heat is not affecting them in any way," she said.

Along with making sure older adults, especially those on medications stay cool and hydrated, Poonja highlighted the importance of safe storage of medications, as instructed by physicians and pharmacists -- room temperature or in a cool, dark place, but not in the refrigerator unless indicated on the label, she said. When medications are kept in hot or humid conditions, such as in a car or a bathroom, they can lose their efficacy. Poonja stressed the importance of talking to health professionals about any concerns over taking medications during periods of extreme heat.

While there hasn't been much research done in the area of medications and heat, Green said the deadly 2021 heat wave in British Columbia put the issue in the spotlight. The BC Coroners Service attributed 595 deaths to the extreme heat event that occurred between June 25 and July 1 that year. Most of the deaths resulted from excessive indoor temperatures in private residences.

Green said almost all who died were over the age of 70 and were living on their own with chronic conditions. 

People living with schizophrenia had a high mortality rate, she noted. A study published in the journal GeoHealth in March last year compared deaths during the so-called heat dome with fatalities during the same period in previous years, and it found a threefold increase among people with schizophrenia.

"So we learned a lot from that event," she said. "But I think, we are learning more about the risk of specific medications when exposed to heat." 

She said it is important to study the relationship between the deaths during the heat waves, heat domes and medications because there is not much known about the scale of the problem.

"We need to adapt to increasing temperatures, because climate change is here to stay. Our bodies are built to cope with a certain degree of heat," she said, and now during extreme heat waves temperatures are exceeding that.

This report by The Canadian Press was first published June 18, 2024.