Heat waves can be deadly. And experts worry that certain medications may make the danger even greater.
Tens of millions of Americans take one or more medications. And many common prescription and over-the-counter medicines, such as certain antidepressants, antipsychotics, antihistamines, and drugs used to treat diabetes and high blood pressure, may reduce the body’s ability to maintain a safe temperature.
The drugs may interfere with the body’s internal thermostat or impair sweating, according to a 2021 review in The Lancet, a peer-reviewed medical journal.
Kenneth Mueller, a pharmacist and clinical instructor at the Emory School of Nursing, says some medications can affect a person’s perception of heat and internal thermostat. And they can alter the body’s ability to redirect blood flow to the skin, a key way that it cools itself.
In hot weather, those side effects could increase the chance of life-threatening consequences, like severe dehydration or heat stroke.
“Doctors and pharmacists should warn patients about the potential dangers of [these] medicines during extreme heat events,” CDC spokesperson Bert Kelly wrote in an email.
Which medications may make heat more dangerous?
Antidepressants like selective serotonin reuptake inhibitors, or SSRIs, may increase sweating, increasing the risk of dehydration.
Others, like tricyclic antidepressants, or TCAs, may decrease sweating, making it harder to cool off.
Antipsychotics may impair sweating and alter the body’s internal thermostat.
Anticholinergic drugs, a large category of medications commonly used to treat an array of conditions such as urinary incontinence, overactive bladder, allergies, and Parkinson’s disease, may interfere with sweating and the body’s internal thermostat. They may also reduce blood flow to the skin.
Patients with heart disease may be prescribed multiple medicines, including diuretics and ACE inhibitors. Such drugs can cause dehydration, affect kidney function, and limit the body’s ability to redirect blood flow.
Dehydration can increase the blood levels of some medications. Even slight increases can lead to toxic effects for certain drugs, such as lithium. These effects can range from tremors and weakness to agitation, confusion, and even death.
And some diabetes medications, including insulin, can lose their effectiveness in hot weather.
Who is most at risk from the interactions between medications and heat?
Anyone can experience a heat-related illness.
But adults age 65 and older and those with chronic conditions are among the most vulnerable to extreme heat.
A study of a 2003 heat wave in France found a 40% increase in excess deaths for people over the age of 65 and a 70% increase in excess deaths for people over 85 during the event. Another found a higher risk of emergency hospitalizations among older people during a 2006 California heat wave.
Older people may be more sensitive to heat because as people age, their sense of thirst can decrease — and so can their ability to sweat.
People with chronic conditions like heart disease and diabetes are also more sensitive to heat. Heart disease can make it harder to move blood to the skin. Diabetes can reduce blood flow to the skin and reduce sweat production. Both processes are essential to keeping the body cool when temperatures rise.
On top of that, older people and those with chronic conditions are more likely to take medicines that lead to more urination and changes in sweating patterns.
Many people over the age of 65 take more than five medications. Some have medication lists in the double digits.
Sixty percent of Americans suffer from at least one chronic disease and 40% have two or more.
In a world of climate-fueled temperature spikes and lengthening summers, the combination of age, chronic disease, and medications can leave people vulnerable.
How to protect yourself in hot weather
If you are at higher risk for heat illness, particularly if you’re older and take medications for chronic conditions, monitor yourself for the first sign of heat stress: feeling dizzy, fatigued, or thirsty.
Make sure you have access to a cool place to rest. Drink non-alcoholic fluids regularly, though follow your doctor’s guidelines — drinking large amounts of plain water in a short amount of time can be dangerous because of the risk of electrolyte imbalance in some people.
Staying in frequent contact with family or other caregivers can also be lifesaving.
But experts interviewed for this article could not offer tips beyond being aware of the potential risks of medication and heat interactions.
“People are on medications because they need them. But what’s the right move when it gets hot out? Is it just stay inside and stay air-conditioned? Is it lower the dose by 10%?” asks pediatrician Aaron Bernstein, director of the Center for Climate Health and the Global Environment at Harvard T. H. Chan School of Public Health. “We don’t know.”
More research needed to understand specifics
Ollie Jay, director of the University of Sydney’s Heat and Health Research Incubator, cautions that researchers have not completed systematic research that shows the exact connection between medications and heat risk.
Although a variety of studies show that people taking certain classes of medications are more likely to need emergency care and that there is a link between certain medications and a higher chance of death during extreme heat events, researchers have yet to perform “gold standard” experiments to demonstrate the exact effect of medications on the body’s ability to respond to heat.
Jay is at work on studies that monitor how an anticholinergic medicine may affect how people regulate their body temperature through sweating and changes in blood flow to the skin.
He adds that there is strong evidence that cocaine affects the sweat and skin blood flow response and reduces a person’s awareness of heat.
“So in terms of evidence for that type of drug, it’s clear, but the prescription medication, there’s not too much out there,” he says.
Bernstein, the pediatrician, agrees that more research is needed to make direct connections between specific prescription medications and the exact contribution to heat illness — and to understand whether the risks to people on multiple medicines are even higher.
“But we absolutely see people who are on these meds showing up in hospitals in greater numbers because the medication is affecting them,” he says.
Health care workers have more to learn
Another challenge: Many health care workers are not aware of the risks of heat and medication interactions. Most do not routinely counsel their patients about how to stay safe.
Cheryl Holder, a primary care physician in Miami, Florida, was tapped in 2021 to co-chair Miami-Dade County’s nascent Climate and Heat Health Task Force. Now Holder wants to ensure that the task force works to develop a local heat action plan that educates the public and health professionals about the health risks from heat, including those from medications.
“Many physicians here have made some of the general changes, where most docs don’t do a lot of diuretics for patients who have to work outdoors,” she says. Because diuretics, commonly known as water pills, can lead to dehydration, their use is especially concerning during heat waves.
“But in terms of a full awareness of the excess mortality and better preparation, we’re just starting to work,” she says.