One day during the summer of 2018, Nita Sweeney, a 58-year-old retired lawyer-turned-author from Upper Arlington, Ohio, set off for a 7-mile run — a normal distance for an avid runner. It was warm at 7 a.m. when she started, and it kept getting warmer. She was sweating heavily, a side effect of the antidepressant she takes. By mile 4, she began to feel light-headed and had to slow down. By mile 6, her heart was pounding, her legs felt like lead and she was nauseated. She felt hot, but her skin was cold and clammy. By mile 7, when she finished, she had stopped sweating entirely — which can be profoundly dangerous on a hot day.

Sweeney was suffering from heat exhaustion, and is convinced her medication — Prozac — had something to do with it.

“The symptoms were frightening, but thankfully not life-threatening,” said Sweeney, author of the memoir Depression Hates a Moving Target: How Running with My Dog Brought Me Back from the Brink. “I’m grateful I didn’t have a much longer run scheduled that day, because I’m stubborn and might have ignored my symptoms in order to complete the mileage.”

Hot days are upon us, and they aren’t likely to ebb anytime soon. Climate change has seen to that. The world is enduring more frequent, prolonged and dangerous heat waves, threatening dehydration, heat stroke and death. And if you are among the millions of Americans who take certain widely used medications — those that control blood pressure, asthma, depression or allergies, for example — you could be facing an additional risk. Drugs can ramp up the risk of heat-related illness and possibly even kill you.

“As medicines that we know can affect our bodies’ abilities to cope with heat are being used more and more, we also know that heat waves are growing stronger,” said Aaron Bernstein, a pediatrician and co-director of the Center for Climate, Health and the Global Environment at Harvard University.

Health affects of heat waves and extreme heat
Source: Nexus Media

“I have taken care of children who may have gotten sick, at least in part, because medicines they had been prescribed affected their body’s ability to deal with heat,” Bernstein added. “We need much more research about if and how medications may be harmful when it gets hot out. Heat waves are getting worse with climate change and medicines that affect our ability to sweat are some of the most widely used. We must understand much more to keep people safe.”

Our average body temperature is around 98.6 degrees Fahrenheit. We keep it constant by producing and losing heat.

“When the outdoor temperature is higher than the skin temperature, the only heat loss mechanism available is evaporation, or sweating,” said Ying Zhang, senior lecturer at the University of Sydney’s school of public health. She said that factors that interfere with this process can cause us to overheat, which could lead to a heat stroke. That could mean especially humid weather, which reduces evaporation, or it could mean drugs that cause us to sweat less, such as the over-the-counter allergy drug Benadryl, or Cogentin, a medication for Parkinson’s disease, or Spiriva, an asthma treatment.

Medicines can make it difficult to cope with heat in numerous other ways. Some, like diuretics, make our bodies lose water, according to Bernstein. Commonly prescribed antidepressants like Prozac can make us sweat more, while other drugs, like antipsychotics, can hamper the brain’s ability to regulate body temperature, he said.

Shawn Morrison, a neurological surgery professor at Oregon Health & Science University who studies how the brain regulates body temperature, pointed out that “our thermoregulatory system does a pretty good job at maintaining a constant internal body temperature.”

Diphenhydramine, an antihistamine sold under the brand name Benadryl. Source: Upupa4me /CC BY-SA 2.0

However, there are several scenarios where a hot environment could affect how patients respond to medicines. For example, when it’s warm outside, you sweat, causing your body to lose water, which lowers your blood pressure. If you are also taking medication to lower your blood pressure, you are at risk of fainting.

While experts are raising alarms about the threat of rising temperatures, few studies have examined the dangerous interaction between drugs and heat. Experts say more research is needed.

“Due to the lack of research in the field, it is impossible to estimate the scale of the problem,” Zhang said. “However, it is for sure that climate change will bring more health problems due to medications.” She said this is particularly true among the elderly, who are likely to be taking more than one drug.

Bernstein said that scientists also need to do more research into how high temperatures could change the chemistry of certain drugs, rendering them less effective.

“I’d be surprised to learn of any medication that was completely stable when exposed to extreme heat, but, at the same time, it’s not always clear how much heat might degrade a medicine,” Bernstein said. “Some medications tend to be carried with people as they get used as needed. One example is albuterol, the most commonly used medicine for asthma. Albuterol inhalers may be less effective when used at high temperatures. We don’t know nearly enough about how keeping a medication in a purse, for example, outside on a hot day, may degrade the medication inside.”

As for Sweeney, she knew how to take care of herself during a heat wave. She quickly got herself inside into air conditioning and stretched out — allowing her heart rate to drop back to normal — and drank electrolyte-rich fluids.

“In central Ohio, where I live, summer days have always been hot and humid, but temperatures rarely rose above 90 degrees,” she said. Now they are routine. So these days, she often starts her runs earlier — especially if a scorcher is coming — or takes her workouts to an indoor track.

“It’s not worth it to wind up with heat stroke,” she said.

Marlene Cimons writes for Nexus Media, a syndicated newswire covering climate, energy, policy, art and culture.