HEAT WAVE HAZARDS

Observer

24-05-2025

Maureen Salamon
With June's arrival, summer heat waves can't be far behind. They're happening more often than ever: according to the Environmental Protection Agency, the average American city experiences six heat waves — prolonged periods of unusually high temperatures — each summer, three times as many as in the 1960s.
Beyond comfort, paying attention to rising mercury levels is vital to our health for a key reason. Certain medications can leave us more vulnerable to heat-related effects or the sun's rays and higher temperatures may render medicines less effective.
Most people don't consider that the weather can amplify drug side effects. "But they should, because it can be dangerous if you don't take the right precautions," says Magie Pham, a primary care pharmacist at Harvard-affiliated Brigham and Women's Hospital.
Tens of millions of Americans take drugs that can change the way they tolerate intense heat and sunshine. Over all, about three-quarters of Americans ages 50 to 64 take prescription drugs, a proportion that climbs to nine in 10 people at 65 and older. The situation is similar with over-the-counter drugs, which adults 65 and up use more than any other age group.
There's no magic number the temperature must reach before this issue becomes relevant. It's relative, Pham says, since people who live in warmer climates year-round typically have different thresholds for how heat affects them compared with those who live in four-season climes. "Every person tolerates heat differently," she says.
Research indicates that people become increasingly vulnerable to heat as they age, since their ability to sweat efficiently and circulate blood to the skin — two key ways the body cools itself — decreases over the decades. (See "Know the signs of heat stress.") Older women are also more physiologically vulnerable to high heat and humidity compared with men of the same age, according to a study published online on August 26, 2024, by the American Journal of Physiology–Regulatory, Integrative and Comparative Physiology.
MEDICATIONS TO WATCH
Known as "water pills," diuretics make us urinate more, removing excess fluids from the body. But these drugs, which are prescribed to manage conditions such as high blood pressure, heart failure, kidney disorders, or glaucoma, can make it more likely you will become dehydrated quickly in extreme heat. They can also lead to imbalances in levels of electrolytes — minerals essential to various bodily functions — which make it harder for the body to regulate its temperature.
"We see many people who've been fine for a long time on diuretics, but then they go somewhere a lot warmer than they're used to and end up becoming severely dehydrated," Pham says. "It's probably the medication I'm most worried about." Other blood pressure drugs. These widely prescribed medications, which include ACE inhibitors, beta blockers and calcium-channel blockers, raise the odds of fainting and falling if they drive blood pressure too low. "If someone is already dehydrated, that can also lower their blood pressure, causing them to faint or fall," Pham says. "It's more of a domino effect from being out in the sun." Doxycycline. This antibiotic is just one example of the many drugs that cause photosensitivity, "meaning you're more likely to get sunburned," she says. "The safest way to avoid that is to make sure you wear sunscreen any time you're going to be outside — even on a cloudy day, because you can still get sunburn." Some antidepressants. Selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) can make you sweat more and impair your body's ability to regulate temperature, hindering your ability to stay cool. "You don't realise how warm you're getting when you're taking these medications," Pham says. "It's important to be hydrated and wear sun-protective clothing, such as a hat, as well as stay in the shade. These approaches can make a real difference in keeping your temperature down." Thyroid hormone. One of the most frequently prescribed medications in the United States, thyroid hormone — usually in the form of levothyroxine (Synthroid, Tirosint, Unithroid) — treats hypothyroidism (an underactive thyroid gland), a condition far more common among women than men. Like other medications above, thyroid drugs can impair the body's temperature regulation, making people sweat too much and increasing the chance of dehydration. Adding to the risk, older people are less likely to realise thirst and sense the degree of heat.
Some over-the-counter antihistamines. Used for allergies and also as a sleep aid, diphenhydramine (Benadryl) and doxylamine (Unisom) may be helpful during the pollen explosion common to hot weather. But like other medicines, they can also hinder sweating and impair core temperature control. Additionally, they raise your risk of sunburn.
Most medication labels direct us to keep the substance in a cool, dry place. That's because elevated temperatures can damage drugs in ways both known and unknown. Insulin, for example, which requires refrigeration, becomes unusable in the heat; inhalers, which are pressurised, can explode; and EpiPens, used to counter extreme allergic reactions, can malfunction.
But scientific studies don't typically examine the effectiveness of drugs beyond room temperature, Pham notes. "If it's 80° or 85°, we have no idea how effective those medications are," she says. "But it makes sense to believe that they're not going to work as well as if they're kept at a more moderate temperature." Plan ahead to avoid exposing your medications to unstable temperatures while you're travelling. On road trips, place medicines in a cooler, not your car's glove box, which can get too hot even if you have the air conditioning on. For plane flights, stash your medications in your carry-on bag, since checked luggage can get lost or delayed and temperatures in a plane's cargo hold can be variable. "Unfortunately, the temperatures where luggage is stored can be too hot or cold," Pham says.
Also, check with your prescribing doctor or pharmacist about how long medications requiring refrigeration can be safely kept at room temperature. And before you fly, Pham suggests calling the Transportation Security Administration toll-free at 866-289-9673 for guidance about medications you'll be carrying, so no snafus arise as you pass through airport security checkpoints. "Your doctor can also provide you with a travel letter to present to TSA representatives so you have no issues," she says. — The New York Times
SIGNS OF HEAT STRESS
- hot, dry skin or profuse sweating
- confusion
- throbbing headache
- loss of coordination
- rapid heart rate
- extreme weakness
- fast, shallow breathing
- nausea and vomiting
- loss of consciousness
- Heat-related drug damage