Are Your Medications Making You More Susceptible to Heat Illness?

Sweating. Shivering. Why do we do it? It’s thermoregulation, of course. Thermoregulation is the biological mechanism responsible for maintaining a steady internal body temperature. If your body can’t do that, it can overheat, leading to hyperthermia. (The opposite is also true: If the core temperature falls below a safe level, it will cause hypothermia.) Both conditions can be life threatening.

A complicating factor in this heat-regulation process is medication. According to Tina George, MD, a family medicine physician with LVPG Family and Internal Medicine–Dunmore, there are many medications – both prescription and over-the-counter – that can affect the human body’s ability to manage high temperatures. Examples are beta blockers used to treat heart conditions, antidepressants and common allergy medicines and antihistamines.

To understand the effect of heat and medication, it’s helpful to look at drugs by class. Here are common medication categories and what can result when the mercury rises. (Generic names of the drugs are used or included in parentheses.)

“It’s important to know how to stay cool – especially for older people.” Tina George, MD

Blood pressure medications:

“Since ACE inhibitors work by keeping our blood vessels from narrowing, they reduce our ability to sweat,” Dr. George says. “If we can’t sweat, we can’t cool down. These drugs also lower blood pressure, so in high temperatures, they can make us more prone to fainting.” Beta-blockers, which treat heart and circulatory problems, can act similarly.

Examples: lisinopril, losartan, metoprolol, aspirin

Diuretics (water pills):

These medicines reduce fluid buildup in the body by helping the kidneys remove salt and water through the urine. “While this lowers the amount of fluid flowing through the veins and arteries, it increases urine production, leading to fluid loss and possible dehydration,” says Dr. George. In this case, she says, it’s important to replace the electrolytes (sodium, potassium and magnesium) that are lost.

Examples: Lasix (furosemide), metolazone

Psychotropics:

Because both antidepressants and antipsychotics fall into this category, the effects in the heat are a mixed bag. Some increase sweating, while others impede sweat production. Some can lower blood pressure and others can affect brain function. “In these two categories of drugs, we have an interference with thermoregulation, and a reduction in thirst,” says Dr. George. “The effects can be varied on top of just feeling hotter and more uncomfortable.”

Examples: Prozac (fluoxetine), Lexapro (escitalopram), Haldol (haloperidol), clozapine

Anticholinergics:

This class of drugs is used to treat a variety of conditions including chronic obstructive pulmonary disease (COPD), incontinence, motion sickness and asthma among others. They essentially block the signals that regulate certain body functions and therefore can reduce sweating and cause your body temperature to rise. “During hot weather, this can make it harder to adapt to the heat,” says Dr. George.

Examples: Scopolamine (scopolamine transdermal), Benadryl (acetaminophen, diphenhydramine, phenylephrine), Dramamine (dimenhydrinate)

When using topical medications (creams or patches) for conditions such as high blood pressure, chronic pain or cancer, individuals should be cautious. “Heat will affect the rate of absorption with these drugs, potentially giving the person a higher level of medicine than what was prescribed,” says Dr. George.

Certain medications can also cause the skin to be super sensitive to sunlight and UV light. Called photosensitivity, it causes skin to burn easily, which can produce a rash or sunburn that can be painful, itchy, blistery and lead to peeling. This can happen with:

• Antibiotics (examples: doxycycline, tetracycline)
• Antifungals (examples: Ancobon, VFEND)
• Antihistamines (examples: Benadryl, Claritin)
• Cholesterol-Lowering Drugs (examples: Zocor, Lipitor)
• Nonsteroidal Anti-inflammatory Drugs (NSAIDs) (examples: Advil, Aleve)
• Oral Contraceptives and Estrogens
• Retinoids (examples: Soriatane, Acutane)

The best course of action in all these situations is to be certain you are taking measures to stay cool.

It’s more than likely that the medications you’re taking are necessary for treating a condition you’re experiencing. Experts say you should not stop taking them. Consult your physician. They may be able to adjust the dose or schedule. Experts also recommend alerting a health care practitioner if you notice any irregular reactions when it’s hot.

“It’s important to know how to stay cool – especially for older people,” says Dr. George. “Many times, they don’t realize how hot it’s getting, or if they’re taking blood pressure medication, they may feel cold.”  

She suggests seeking out shade and having access to air-conditioned spaces such as restaurants and grocery stores, or senior centers for the elderly. If you don’t have an air-conditioned space, Dr. George’s advice is “to head for the mall or the sprinkler.” She also recommends staying hydrated with electrolytes, using electrolyte drinks, powders and tablets.

Finally, Dr. George recommends planning ahead. “These days, the car is a pressure cooker, especially if it’s been sitting out in the sun. If you know you’re going to be driving somewhere, start the car ahead of time and turn on the air conditioner. Behavior and environmental adaptations are great for keeping yourself safe.”

For more guidance, visit Heat and Medications - Guidance for Clinicians (cdc.gov)