Your medications might make it harder for you to beat the heat

The pills stocked inside your medicine cabinet may factor into how well you can handle summer heat.

Extreme heat can be deadly. As outdoor temperatures sizzle, our bodies jump into action to keep internal temps under control (SN: 8/6/23). Blood rushes to the surface of our skin to release heat as sweat pours onto it, cooling us as it evaporates. If these methods fail to keep body temperature in check, people can fall victim to heat-related symptoms such as headache, dizziness and confusion. In severe cases, people might become delirious or go into organ failure.

For some, chronic health conditions can add an extra one-two punch when it comes to regulating body temperatures. Not only do some conditions affect physiological cooling, but the medications that treat those diseases could also interfere with the body’s air conditioning. Older people are especially vulnerable to these effects, both because they face higher rates of some chronic conditions and because the body’s ability to cool itself down decreases with age.

Cardiovascular medicines, antipsychotics and other drugs have been linked to an increased risk of hospitalization during heat waves. But researchers don’t have a solid understanding of which medicines pose the greatest threat or the mechanisms behind potential risks. Some drugs might interfere with sweat and blood flow. Others may influence the body’s fluid levels, which ensure that we can safely keep producing sweat and pumping blood.

Pinpointing which medications might dangerously tweak physiology is tough, says Soko Setoguchi, an epidemiologist at Rutgers University in New Brunswick, N.J. That’s because people are typically taking prescriptions to treat a disease, so “it becomes important to tease out if [vulnerability to the heat comes from] the disease or drug.” Ethical considerations, such as taking people off life-sustaining medications, make conducting randomized studies among patients difficult.

But the risks are growing. For people who depend on medications to manage disease, “hotter weather brought on by climate change represents a serious health risk,” says Jericho Wee, a thermal physiologist at the National University of Singapore’s Yong Loo Lin School of Medicine. What’s more, the World Health Organization estimates that the share of adults older than 60 in the global population is expected to roughly double by 2050 compared with 2015. There’s a sense of urgency to understand how medications interact with heat, Wee says. 

Some heart and brain medicines mess with the body’s cooling system

To begin to get a handle on how drugs and diseases are affected by heat, Setoguchi and colleagues dug into the records of nearly 10,000 Medicare patients age 65 and older and found that antipsychotics and cardiovascular drugs were among those linked to heat-related hospitalization. Even in the absence of heat waves, some drugs, such as diuretics, were associated with a higher risk that patients would be hospitalized for heat-related illness, the team reported in PLOS One in 2020.

Chlorpromazine, an antipsychotic used to treat psychiatric conditions including schizophrenia, is one example of a drug that may make cooling off challenging. The medication can suppress sweating and divert blood flow away from the skin, Wee says. It can also impair the body’s internal thermostat, leading to an increase in body temperature.

Other antipsychotic drugs may have similar effects. A 2021 case report of a 47-year-old man taking risperidone and fluphenazine for schizophrenia and hospitalized for heat illness suggested that the drugs altered the man’s brain chemistry in ways that may have made his body less likely to recognize that he was thirsty and overheating. He was successfully treated to bring down his body temperature and sent home.

Heart disease treatments can also make patients more vulnerable to heat, Wee says. Beta blockers used to treat high blood pressure and antiplatelet drugs that prevent blood clots can reduce the amount of blood that rushes to the skin to release heat into the surrounding air. And taking diuretics, common medications for heart failure that help the body flush out excess fluid that would otherwise pool in the lungs and ankles can lead to dehydration if people don’t replenish that fluid loss in extreme heat, Wee says. Dehydration also causes less blood to flow to the skin.

There’s no solid evidence to suggest that people should stop taking or reduce doses of medication in extreme heat, Setoguchi says. “People are taking medications because they need them.” Instead, people should talk to their doctors about ways to avoid heat and learn what to do in cases of heat stress. 

What are the challenges to studying heat, health issues and medicines?

While studies are beginning to reveal how brain and heart medicines might impact temperature regulation, there are myriad other drugs with unknown effects in extreme heat, says Jason Lee, an exercise and thermal physiologist at the Yong Loo Lin School of Medicine. That includes treatments for diabetes and cancer.

Researchers can make assumptions about how a drug might impact the body’s response to heat based on what’s known about how the drug works. But how these processes interact with our complex physiology in heat is still relatively unknown, says Nicole Vargas, a thermal physiologist at Australian National University in Canberra. “It’s one thing for clinicians and pharmacists to say, ‘Hey, this drug acts on the hypothalamus. We know that the hypothalamus is really important in a lot of our thermoregulatory functions. It must act on thermal regulation.’ But what does that mean?”  

Part of the difficulty in finding answers is that there are ethical and practical challenges, Lee says. For one, it’s unethical to run randomized clinical trials that stop treatment for a group of patients who depend on medications to handle their disease. For another, “you cannot really randomize heat [waves],” Setoguchi says.

Some researchers have tried giving medications to otherwise healthy people and comparing their heat tolerance to that of those not on the drug. For instance, researchers at the University of Sydney’s Heat and Health Research Incubator are exploring whether antidepressants affect how the body handles heat in people without depression, Vargas says.

But such work leaves out the underlying conditions that could be compounding how heat interacts with a drug. Case studies can help, Setoguchi says, particularly those that follow many patients, comparing when each patient takes the drug versus when they don’t. So can studies that include people taking a different medication for the same condition. Still, disease severity varies among people. Someone with worse symptoms may be more vulnerable to heat than someone with milder disease who doesn’t take medications, clouding how researchers might interpret results.

It’s important to consider everything together, from the disease to the specific medication a patient is taking, Setoguchi says. This could help clinicians predict who might face the most danger in extreme heat. For now, though, the race is on to better understand which medications researchers should focus on.