Medications Can Raise Heat Stroke Risk. Are Doctors Prepared to Respond as the Planet Warms?

As climate change brings dangerous heat waves, too little is being done to better warn patients or physicians of the growing risk, medical experts say.

A medical team in Orange, California, with a doctor as the test subject, tests the impact of rising heat inside a car on the human body. Credit: Frederic J. Brown/AFP/Getty Images
A medical team in Orange, California, with a doctor as the test subject, tests the impact of rising heat inside a car on the human body. Some types of medication can affect how the body responds to heat. Credit: Frederic J. Brown/AFP/Getty Images

Share this article

This story was co-published with The Weather Channel as part of Collateral, a series on climate, data and science. 

On a hot day in Boston, a young boy arrived in Dr. Aaron Bernstein’s emergency room with chills and signs of confusion. He had overheated while playing outside, and he wasn’t sweating enough to properly cool down.

The boy, who has autism, was taking several medications — Seroquel, Cogentin and Benadryl — all of which can change the body’s response to heat. 

In a city like Boston, which has experienced only a handful of 100-degree days over the past century, the danger associated with abnormally high temperatures, including how medications factor in, might not be immediately obvious. 

“It is not a part of our culture to think of heat as risky,” said Bernstein, a pediatrician at Boston Children’s Hospital and co-director of the Center for Climate, Health, and the Global Environment at Harvard’s School of Public Health.

As global temperatures rise and extreme heat waves become more common, so does heat illness. But while doctors have known for decades about the adverse effects of some medications on how the body regulates temperature, little is being done in the U.S. to better warn patients or physicians of the growing risks associated with climate change, doctors, researchers and community health experts said. 


We deliver climate news to your inbox like nobody else. Every day or once a week, our original stories and digest of the web's top headlines deliver the full story, for free.

Medications that are widely used to treat conditions from high blood pressure to mental health disorders can affect the ability to regulate heat. They can alter the body’s ability to sweat, change how it regulates temperature or cause dehydration, all impairing people’s capacity to deal with rising temperatures and heat waves.

Doctors may be aware of the risks of some medications in extreme heat, but health experts say many stop short of linking the risk to the increasing heat and humidity resulting from climate change. 

“The message that needs to be made clear to everyone is that climate change is making it harder for me to do my job as a doctor,” Bernstein said. 

It’s not unusual for someone to be taking five medications that each change the body’s ability to deal with heat, and doctors and patients both need to be aware of the risks, said Amy Collins, an emergency medicine doctor at MetroWest Medical Center in Massachusetts and senior clinical adviser for Health Care Without Harm.

Diuretics, used to treat high blood pressure, can cause people to become dehydrated more easily. Some over-the-counter allergy drugs reduce sweating, an important cooling mechanism. Some mental health medications make a person feel less thirsty, meaning he or she could forget to stay hydrated. 

Infographic: Medications + Hot Weather Can Cause Problems

Medications can also multiply existing heat risks: Diuretics, for example, are often prescribed to older adults, who are already at a higher risk of getting sick in the heat.

Older adults, children and economically disadvantaged groups are particularly vulnerable to heat, according to the U.S. government’s Climate and Health Assessment. The report predicts an increase of “thousands to tens of thousands of premature heat-related deaths in the summer” by the end of the century as a result of climate change.

“I think there are still physicians who aren’t making the link between heat waves and climate change,” Collins said. There’s a “huge gap” when it comes to doctors discussing climate change with patients. 

Known Risks, But Research Fell Off 

In 1999, an intense heat wave swept the midwestern and eastern United States. 

A 24-year-old man was found dead in his Dayton, Ohio, apartment. He had a history of mental illness and depression and had been taking benztropine, which can decrease sweating. 

In Cincinnati, a 34-year-old woman who had schizophrenia died of heat stroke in her group home; her core temperature was over 106 degrees Fahrenheit. She had been prescribed furosemide, a diuretic. 

In a report on the heat wave deaths, the Centers for Disease Control and Prevention (CDC) described several medications that can increase the risk of hyperthermia and heat-related death, including antipsychotics, major tranquilizers, antidepressants, antihistamines, drugs used to treat Parkinson’s disease and some over-the-counter sleep medications. But its recommendations focused more broadly on better education about heat risks and better monitoring for people at risk.

“One of the lessons we learned is that it is not enough to simply monitor,” Malcolm Adcock, Cincinnati’s health commissioner, told the Dayton Daily News at the time. “We need a preventive strategy that would allow temperatures to be maintained appropriately.”

The CDC conducted several studies in the early- and mid-2000s, including a 2001 paper on the impacts of climate variability on health and a 2008 report on climate change and extreme heat. But when asked about relevant research since then, the CDC communications office responded “we don’t currently have experts working on this specific area of research.”

Twenty years after the Ohio report, medical professionals say awareness and training in how medications can affect how the body reacts to heat are still lacking in the U.S.  

Chart: Heat's U.S. Death Toll

“We’ve known for a long time that people whose sweat glands aren’t working properly could die of heatstroke,” said Dr. Susi Vassallo, an emergency medicine doctor at Bellevue Hospital in New York City and professor at New York University who has studied the effect of drugs on the body’s ability to regulate heat. 

But standard medical response procedures for people suffering from heat stroke that could include checking for medications that can play a role are largely missing from U.S. hospitals, Vassallo said. 

In Europe, the World Health Organization’s regional office has published guidelines for health professionals responding to heat as concerns increase with global warming. The guidelines suggest doctors give patients a “pre-summer medical assessment,” including advising them on “medication relevant to heat.”

It recommends doctors consider adjusting medication dosages during hot weather as needed. Those decisions should be made on a case-by-case basis, as there are no standards or formal advice for changing medications during hot weather, it says. 

Developing Heat Stoke Response Standards

Vassallo is working with medical toxicology fellows at the New York City Regional Poison Control Center to draft national standards for emergency medicine physicians responding to heat stroke, similar to medical responses already in place for heart attacks, strokes and sepsis. She hopes to raise doctors’ awareness of the signs, treatments and factors, like chronic illness and medication, for heat stroke. 

Public health preparation means creating an action plan, she said, not just issuing warnings ahead of heat waves. 

“Knowing heat is coming is different from knowing where our vulnerabilities lie,” Vassallo said.  

Patients, too, need to be aware of the heat risks the medications they’re taking may carry. Heat stroke doesn’t tend to progress step-by-step, Vassallo said: “It can be very sudden and catastrophic.”

“You can be bicycling and have taken an anti-cold medication … and go from feeling fine to heat stroke within a matter of minutes,” Vassallo said. 

Doctors and pharmacists should “re-emphasize” heat risks to their patients, said Julia Gohkle, an associate professor of environmental health at Virginia Tech and the University of Maryland. Warnings each year in late spring, for example, would help to remind people who may have forgotten about a medication’s side effects over the winter. 

Ways Medication Exacerbates Heat Risk 

Prescription medications can affect the body’s response to extreme heat in a number of different ways. The effect varies by person, with dosage and other drugs also playing a role. Some of the major mechanisms include:  

  • Dehydration: Diuretics (commonly called “water pills”) help the body to get rid of salt to treat high blood pressure. They tend to increase urination, which can cause dehydration. Laxatives, some antibiotics and medicines used to treat cancer can also dehydrate people since they can cause diarrhea.
  • Reduced sweat: Sweat is one of the most important tools the body uses to cool off, so medications that impair sweating increase the risk of overheating. Some mental health medications, such as antipsychotics, anticholinergics and beta-blockers, and some allergy drugs, among others, can have this effect.
  • Thirst and heat recognition: Some antidepressants and blood pressure medications can decrease thirst, making it difficult for people to remember to stay hydrated.
  • Blood pressure and vasodilation: When the body gets too warm, it pumps blood toward the skin to release heat. To help blood flow, blood vessels expand, a process called vasodilation. Some blood pressure and other medications affect vasodilation, inhibiting the body’s ability to cool off.
  • Heat generation: Some medications produce heat by affecting the hypothalamus, a part of the brain which sets normal body temperature.

People Most at Risk Are Often the Least Mobile

People can reduce the risk of heat illness by keeping cool in air-conditioned buildings. But many of the people most at risk are those who are stuck: Mobility issues might make it difficult to get to air conditioning, or the cost of air conditioning means it doesn’t get used.

People who are incarcerated or homeless — many of whom are taking mental health drugs — are some of the most at risk for heat stroke. 

Vassallo has done extensive work analyzing heat risks in prisons, many of which don’t have air conditioning, even across the South where summer temperatures can become dangerous. There are “a significant number of heat-related deaths in prisons,” she said. But prisons aren’t required to report heat deaths to the Bureau of Justice Statistics, which tracks other causes of death in prisons, including suicide and accidental injury.

In communities, offering cooling centers, where people can spend time in air conditioning, could help; but the centers often aren’t well-advertised. 

“You pretty much have to have the internet available to you to find one,” Vassallo said. 

Published Aug. 20, 2019