“Hot as hell” is a phrase we have heard a lot this summer. And with good reason. Temperatures have soared in much of the country. And it’s not over yet. Anyone without air conditioning has really been suffering. So has anyone who has to work or participate in sports outside. Heat stroke is a very real danger and it can be life threatening. There is another serious problem: heart attacks! Some very commonly prescribed medications may be more dangerous in hot weather because they are linked to an increased risk for heart attacks (Nature Cardiovascular Research, Aug. 1, 2022). A doctor who prescribes a medication in November or February would probably not warn a patient about the dangers of heat and humidity.
Who Is Vulnerable?
Military personnel, firefighters, telephone linemen and athletes are all warned to recognize the early signs of dehydration and overheating, which include dizziness, nausea, confusion, headache or changes in speech or behavior.
There is another group that is often forgotten, however, and it includes tens of millions of Americans. Older people and those who take certain medications are especially vulnerable to both heat exhaustion and heat stroke.
Why Are Some Drugs More Dangerous in Hot Weather? No Sweat!
Part of the problem with many medications is sweat, or more precisely, the lack of perspiration. As moisture evaporates from your skin, it helps cool down the body. Slow or stop the sweating process and you are quickly headed for overheating. Blood flow to the skin is also crucial for the cooling the body.
To better understand this process it helps to imagine your car on a hot day. The way your automobile cools its engine is through air flow. Hot water from your motor passes through coils in the radiator. As you drive, air passes through the coils and cools down the liquid that then recirculates through the engine. Disconnect the radiator and the engine overheats.
When people can’t circulate blood to the skin adequately or sweat efficiently, the core temperature of the body may rise and put people at risk. A wide variety of drugs are dangerous in hot weather because they interfere with the body’s natural cooling process.
This reader describes what it’s like to feel too hot:
Q. Reading your article about medicines that are risky in hot weather helped me make sense of my experience. I often feel too hot and have trouble with sweating.
Because I have fibromyalgia, chronic pain syndrome and arthritis, I have been taking gabapentin and amitriptyline as well as some other meds. Even in the depths of winter, I can be found with few bedclothes on because I feel too hot! It drives my partner mad as he feels the cold intensely. What do I need to know about these drugs in the summer?
A. Antidepressants like amitriptyline are especially troublesome in hot weather. Some people are prescribed amitriptyline off label for insomnia, fibromyalgia or nerve pain.
When you make it hard for the body to sweat due to the anticholinergic activity of amitriptyline, it loses some ability to cool down. That’s especially true when it is hot and humid. Reducing perspiration makes hot weather riskier.
Please do NOT stop any of your medications suddenly. That could precipitate unpleasant withdrawal symptoms. Your best strategy would be to stay out of the sun and try to keep as cool as possible.
Other Drugs That Reduce Sweating and Can be Dangerous in Hot Weather
Drugs that decrease sweating are far more common than most people realize. Antidepressants that interfere with a chemical called acetylcholine are especially problematic. This anticholinergic effect slows sweating substantially. These medications include amitriptyline, desipramine and doxepin.
Pills for overactive bladder such as Detrol, Ditropan or Toviaz also have this kind of effect. Many antihistamines have anticholinergic activity as well. Diphenhydramine is of particular concern because it is found in OTC products like Benadryl as well as PM pain relievers like Advil PM or Tylenol PM.
There are dozens and dozens of medications with anticholinergic activity. Many health professionals may not recognize all the drugs that have this kind of activity. We worked hard to put together just such a list. Here is a link to that list.
Heart Attacks:
Does Your Doctor Know Which Drugs Could Be Dangerous in Hot Weather?
Researchers at Yale and in Germany teamed up to to determine whether medication use could affect heart attack risk during extreme heat exposure. They analyzed data from Augsburg, Germany between 2001 and 2014. There were nearly 2,500 heart attacks during the hot weather months. What they found will surprise most physicians.
The investigators reported significant heat-related heart attack risks among patients taking both anti-platelet medication and beta blockers. What are anti-platelet drugs? The most common is aspirin. It works by preventing the sticky part of blood (platelets) from clumping together to create a clot.
Some other anti-platelet medications include clopidogrel, ticlopidine and prasugrel. The authors did not name specific drugs in the category, though. It is important to note, however, that people with stents and underlying heart disease are often prescribed anti-platelet drugs to prevent a blood clot that could lead to a heart attack.
Beta blocker heart drugs include atenolol, carvedilol, metoprolol and propranolol. The last time I checked, such drugs were taken by 25 million Americans every day. If people were taking both an anti-platelet drug and a beta blocker together (a not uncommon situation), their risk of a heat-related heart attack was 75 percent higher.
Are Statins More Dangerous in Hot Weather?
Here is the kicker in the research published in the journal Nature Cardiovascular Research, Aug. 2022. In a surprising observation, statins tripled the heart attack risk on very hot days, but only among people under 60 years old.
I know that this will come as a shock to most health care professionals.
That is why I quote the researchers’ findings precisely:
“In addition, among younger patients, significant heat-related risk for non-fatal MI [heart attack] was observed among users of statins (OR [odds ratio]=3.39 but not among non-users (OR=0.84), with the OR among users significantly higher than the OR among non-users (P<0.01).”
When something increases a risk three fold, it is usually considered quite concerning. The authors probably recognized that this statin finding was a hot potato.
Maybe that is why they did not include it in the final paragraph:
“In summary, we found that patients taking anti-platelet medication or beta-receptor blockers may be more vulnerable than patients not taking these medications to non-fatal MI risk due to heat exposure. Our findings, if confirmed, can help clinicians, patients and public health officials develop targeted strategies to reduce the burden of cardiovascular disease under climate change.”
People who were not taking these drugs were at no higher risk for heart attacks, even when temperatures were high. One hypothesis for the beta blocker effect is that such drugs interfere with heat dissipation through vasodilation. If there is a lesson to this research, it would be that people taking anti-clotting drugs, beta blockers and statins should be extra careful when temperatures soar.
Conflicting Data:
A recent study published in Pharmacoepidemiology and Drug Safety (June, 2024) contradicts the study described above. This epidemiological study concluded that statin treatment “…may be associated with a reduced risk of death during extremely hot days, particularly among men.”
Confusing? You bet. There has been very little published research about medication-related heart attacks during hot weather. We wish there were more we could share with you on this “hot” topic.
More Medicines That Pose Risks When Temperatures Soar:
Decongestants that contain pseudoephedrine are another problem. You frequently find this ingredient as the “D” (for decongestant) in allergy medication such as Allegra-D, Claritin-D or Zyrtec-D. The vasoconstrictor action of pseudoephedrine may reduce blood flow to the skin, making it a little harder for your body’s radiator to dissipate heat.
Antipsychotic drugs are now prescribed for conditions other than schizophrenia. Medications such as Abilify and Zyprexa are increasingly used to treat depression, bipolar disease, dementia and personality disorders. Such drugs may also be dangerous in hot weather since they make it harder for the body to cool down when temperatures climb.
We have barely touched the surface when it comes to all the medicines that make people vulnerable to high heat. When temperatures hover around triple digits, it is crucial for those on medications to check with a pharmacist to make sure that their pills aren’t putting them at risk for heat stroke.
NEVER Stop Your Medicine!
No one should ever stop taking a medication suddenly, especially in hot weather. That is doubly true for anti-platelet medications and beta blockers! Doing so could trigger a heart attack, which is the last thing anyone wants. But knowing that extreme heat can increase the risk means that people will need to be extra careful about not spending time outside in the middle of the day.
People under the age of 60 who are taking statins such as atorvastatin, lovastatin, pravastatin, rosuvastatin and simvastatin should also be cautious when going outside in hot weather. If you are going to exercise, please be especially vigilant to stay hydrated and not get over-heated!
Heat Stroke vs. Heat Exhaustion:
When the body can’t cool down properly, the consequence may be heat stroke. It is easy to confuse heat stroke and heat exhaustion, but they are different. Heat exhaustion is due to fluid loss. This may occur if someone doesn’t drink enough water to replace what has been lost in sweating. The person becomes weak and may feel nauseated, anxious and lightheaded. The pulse may be weak and slow, the blood pressure low and the skin pale and clammy.
That person was sweating too much. Heat stroke, on the other hand, happens when a person can’t sweat enough to cope with extreme temperature. The onset of symptoms may be sudden, with headache, weakness and disorientation signaling an imminent loss of consciousness.
The skin is hot, USUALLY dry, and flushed. The pulse is fast and hard, and the body temperature is elevated. Besides people taking anticholinergic medicines, children, older people and pets are vulnerable. Some have died from heat stroke when they were left in a closed car. HEAT STROKE REQUIRES IMMEDIATE EMERGENCY MEDICAL ATTENTION.
Learn More and Share:
If you would like to know more about medicines that have anticholinergic activity, we have compiled a list here. Please share your own experience with medications and hot weather in the comment section below.
You may also want to send this article to friends and family. We suspect that someone you know is taking a beta blocker, an anti-platelet medicine or a statin. They (and their health care providers) may not know about the potential connection between such drugs, very hot weather and heart attacks. It’s super easy to share. Just scroll to the top of the page and click on the icons for email, Twitter and Facebook.
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