Summer is in full swing—and there’s another heat wave slamming your area. You’re ready to hit the beach to cool off. As long as you remember to reapply sunscreen and stay hydrated, you’re enjoying the hot temperatures safely…right? Not so fast! If you take any daily pills—prescription or over-the-counter—check with your pharmacist first. Certain medications that cause heat intolerance can ruin a day of fun in the sun, and have dangerous side effects as temperatures skyrocket.
What is heat intolerance?
Also known as hypersensitivity to the heat, heat intolerance is more than just feeling uncomfortable when temperatures rise. It’s a condition that occurs when your body can’t regulate its temperature properly.
As it gets hotter outside, the hypothalamus in your brain sends messages through your nerves that tell your skin to cool off by sweating. When the moisture evaporates off your skin, it decreases your core temperature. If something disrupts this process, your body is unable to cool down—and that can lead to unpleasant symptoms like nausea, dizziness, or even a heat-related illness.
Heat intolerance has many causes: certain health conditions, age, weight, and—you guessed it!—the medications that you take.
6 medications that cause heat intolerance
There are several types of medications that can increase your sensitivity to the heat.
1. Blood pressure medications
There’s a risk between heat and high blood pressure medications. Certain prescription treatments for high blood pressure, also known as hypertension, can make you more susceptible to heat intolerance. This is especially true for two types of medications: thiazide diuretics and beta blockers.
Thiazide diuretics and heat intolerance
“Certain medications, called diuretics, force fluid out of our bodies through our kidneys to control high blood pressure and heart failure,” says David Cutler, MD, family medicine physician at Providence Saint John’s Health Center in Santa Monica, CA. “These medications could cause dehydration, a potentially grave danger in hot weather.” Thiazide diuretics, such as chlorthalidone and Microzide (hydrochlorothiazide), are known to have this effect.
Beta blockers and heat intolerance
Beta blockers, such as Toprol XL (metoprolol) and Inderal (propranolol), can decrease blood flow to the skin, which can inhibit sweating. “It mainly has to do with how the blood flows to the skin,” says Dawn Shill, Pharm.D., a pharmacist for the Veteran’s Affairs Healthcare System in Anchorage, Alaska. “The blood vessels don’t dilate as they should to allow heat to escape. with certain blood pressure medications. By constricting blood flow, the body can’t regulate temperature as much.”
Both effects make it harder for your body to cool off.
You take a daily dose of an antihistamine such as Benadryl (diphenhydramine) to manage your seasonal allergies. This over-the-counter treatment is very effective at stopping sniffling, sneezing, and itchy eyes. But, did you know some of the same medications can prevent you from sweating? Combine that with the summer sun, and it can increase your chances of overheating. This effect is more common with first-generation antihistamines, like Benadryl. Second-generation antihistamines, such as Claritin, Zyrtec, and Allegra do not have this effect.
“Antihistamines produce an anticholinergic effect commonly referred to as a ‘drying’ effect,” explains Kristi Torres, Pharm.D., a member of the SingleCare Medical Review Board. “The same mechanism that allows antihistamines to slow mucus production is also responsible for your body producing less sweat. When your body is not able to sweat, it is difficult to regulate your internal temperature in the face of high external temperatures.” If this is a concern, ask your doctor or pharmacist to help you select an appropriate antihistamine.
RELATED: Can I take antihistamines everyday?
Getting sick is likely the last thing you’re thinking about in the summer. But, colds can strike year-round, even in warm weather. If you’re all stuffed up and reaching for the Sudafed (pseudoephedrine), you may need to postpone your pool day for some good old fashioned rest and relaxation.
“Decongestants work the same way as blood pressure medications, decreasing the blood flow to the skin,” Dr. Shill says. That can be dangerous on an already hot day.
4. Overactive bladder treatments
Anticholinergics block the action of involuntary muscle movements that can make you feel like you need the restroom when you don’t. That’s a positive when you’re dealing with a urinary tract infection, incontinence, or poor bladder control. Unfortunately, they have a side effect that can spell trouble in the summer. Medications like Ditropan (oxybutynin) or Detrol (tolterodine) can reduce sweating which reduces your ability to cool off.
5. Stimulant medications for ADHD
Certain prescriptions that treat attention deficit hyperactivity disorder (ADHD) fall into a class of medications known as stimulants. This includes well-known Rx’s such as Adderall (amphetamine/dextroamphetamine) and Ritalin (methylphenidate). These medications raise your body temperature, increasing risk for heat intolerance.
On top of that, they physically constrict blood vessels and reduce blood flow to the skin. “In the heat, blood flow needs to be increased to the skin in order to cool the body down,” explains Anthony Puopolo, MD, board-certified physician and chief medical officer of LifeMD. Stimulant medications can prevent that reaction.
6. Psychiatric medications
Medications used to treat certain mental health conditions and Parkinson’s disease all have one thing in common: They affect the hypothalamus. Since this region of the brain is essential to cooling, they can inhibit your ability to reduce body temperature on hot days. These medications can also decrease your thirst reflex, increasing dehydration.
There are many different types of psychiatric prescriptions that can lead to heat intolerance:
- Tricyclic antidepressants such as Elavil (amitriptyline) and Pamelor (nortriptyline)
- Antipsychotics such as Haldol (haloperidol) or Thorazine (chlorpromazine)
- Dopaminergics such as Sinemet (carbidopa/levodopa)
If you take any of the above, talk to your healthcare provider or pharmacist before planning a picnic in the heat of the day.
What signs of heat intolerance should you watch for?
The first sign of heat intolerance is feeling hot and uncomfortable. In addition, you might experience symptoms such as:
- Nausea or vomiting
- Flushed skin
When these signs appear, take steps to go indoors and cool off as soon as possible. Remove excess clothing, take sips of cool water, and place cool compresses on your body.
If you remain in the heat, you could develop symptoms such as rapid breathing, decreased sweating, or altered mental state. “A person should seek medical care if they are experiencing the aforementioned symptoms,” Dr. Puopolo says. These symptoms can mean that your heat intolerance is progressing to a heat-related illness, such as heat stroke, which may be fatal when untreated.
How to prevent heat intolerance
Prevention is always the best treatment. If you are on any of the medications known to increase the risk of heat intolerance, take extra precautions before you head outdoors:
- Carry water with you and drink it regularly to stay hydrated.
- Wear a hat to keep excess sun off of your body.
- Avoid spending prolonged periods outdoors during the heat of the day.
- Wear loose fitting, lightweight clothing.
- Avoid exerting yourself too much when it’s hot.
When in doubt, drink a glass of water and sit down for a minute indoors. If your symptoms don’t subside quickly, it may be time to seek medical treatment. Be sure to keep a list of medications you are currently taking handy so that your treating physician can respond appropriately.