Heat Exposure Precautions with Diuretics and Anticholinergics

When the temperature rises, most people think about drinking more water, staying in the shade, or wearing light clothes. But for people taking diuretics or anticholinergics, heat isn’t just uncomfortable-it can be life-threatening. These medications, commonly prescribed for high blood pressure, heart failure, overactive bladder, and depression, interfere with the body’s natural ability to cool down. And many people don’t even realize it.

How Diuretics Put You at Risk in the Heat

Diuretics-often called water pills-help your body get rid of extra fluid. That’s why they’re used for high blood pressure and heart failure. Common ones include furosemide (Lasix), hydrochlorothiazide (Microzide), and chlorthalidone (Hygroton). But in hot weather, they work against you.

These drugs make you pee more. That sounds helpful, but when it’s hot, your body needs every drop of fluid to sweat and cool down. Diuretics drain that away. You lose sodium, potassium, and water faster than your body can replace it. That leads to dehydration, low blood pressure, dizziness, and even heart rhythm problems.

A 2022 study of over 1.2 million Medicare patients found that people on loop diuretics had a 37% higher chance of being hospitalized for heat-related illness during summer months-even when temperatures were just above 80°F (26.7°C). That’s not a heatwave. That’s a warm Tuesday. And the risk doesn’t wait for extreme weather. It shows up when you’re gardening, walking the dog, or sitting in a car with the windows up.

Why Anticholinergics Block Your Body’s Cooling System

Anticholinergics are another group of drugs that quietly increase heat risk. They’re used for overactive bladder (oxybutynin, tolterodine), Parkinson’s, depression (amitriptyline), and even allergies. But here’s the problem: they stop your body from sweating.

Sweating is your body’s main way of cooling off. Anticholinergics block the chemical signal (acetylcholine) that tells your sweat glands to activate. Studies show that strong anticholinergic drugs-those with an Anticholinergic Burden Score (ACB) of 3-can reduce sweating by 30% to 50%. That means your body can’t cool down, even if you’re outside in 90°F heat.

The CDC lists anticholinergics as one of the top medication classes linked to heat-related deaths. During the 2021 Pacific Northwest heat dome, 63% of people who died from heat exposure were taking either a diuretic or an anticholinergic. Many of them didn’t feel sick until it was too late. Why? Because these drugs can also cause confusion, dry mouth, and drowsiness-symptoms that look like heat exhaustion but are actually caused by the medication itself.

The Combined Danger: When Medications Multiply Risk

Most people don’t take just one of these drugs. Older adults often take multiple prescriptions. A 75-year-old with high blood pressure might be on hydrochlorothiazide. If they also have an overactive bladder, they might be on oxybutynin. And if they’re dealing with chronic pain or depression, they could be taking amitriptyline. That’s three medications, all working together to shut down your body’s ability to handle heat.

This isn’t theoretical. In a 2023 study published in the Journal of Thermal Biology, researchers found that people taking multiple medications with anticholinergic effects showed no ability to regulate core body temperature during heat exposure-even if each drug alone seemed mild. The effects add up. It’s not just the drugs. It’s the combination.

And here’s the scary part: you might not feel anything wrong until your body starts shutting down. No sweating. No thirst. Just confusion, weakness, or fainting. That’s why many heat-related deaths happen indoors, in homes without air conditioning, with people who don’t realize they’re in danger.

What You Should Do-Practical Steps That Work

You don’t have to stop your medications. But you do need to adjust how you live during hot weather. Here’s what actually helps:

• Drink water-even if you’re told to limit fluids. If you’re on a diuretic for heart failure, your doctor may have told you to restrict water. That’s fine in normal weather. But in heat, your body needs more fluid to sweat and survive. Talk to your doctor about temporarily increasing your fluid intake during hot spells. Don’t guess. Ask.
• Check your sweat. If you’re on an anticholinergic and you don’t sweat-even when it’s hot and you’re moving-you’re at risk. Your body isn’t cooling. That’s a red flag. Stay indoors, use fans, and avoid physical activity during peak heat hours (10 a.m. to 4 p.m.).
• Wear the right clothes. Light-colored, loose, breathable fabrics help. Dark clothes absorb heat. Tight clothes trap it. Cotton and linen are better than polyester. And wear a wide-brimmed hat. Sunscreen matters too-many anticholinergics make your skin more sensitive to sunburn.
• Use a buddy system. If you’re over 65, take anticholinergics, or have memory issues, have someone check on you twice a day during heat events. Call. Text. Drop by. Because if you’re confused from the medication or the heat, you won’t know to ask for help.
• Know the warning signs. Headache, nausea, dizziness, muscle cramps, rapid heartbeat, confusion, or dry skin with no sweat. These aren’t just “feeling off.” These are signs your body is failing. Call 999 or go to A&E immediately.

Don’t Stop Your Meds-But Talk to Your Doctor

Never stop taking diuretics or anticholinergics on your own. Stopping suddenly can cause your blood pressure to spike, your heart to struggle, or your bladder to become uncontrollable. That’s dangerous too.

Instead, talk to your doctor before the next heatwave. Ask:

• “Do any of my medications make me more sensitive to heat?”
• “Should I adjust my dose during summer?”
• “Is there a safer alternative for my condition?”

Some doctors are already doing this. In a 2022 pilot study at Massachusetts General Hospital, 42% of heart failure patients on diuretics had their doses temporarily lowered during a summer heatwave-under medical supervision. Their symptoms improved. Their hospital visits dropped.

The Bigger Picture: Climate Change Is Making This Worse

The UK is getting hotter. The number of days above 90°F (32.2°C) has increased by nearly 50% since the 1970s. Heatwaves are longer, more frequent, and more intense. And as the population ages, more people will be taking these medications.

The CDC and the Environmental Protection Agency now recognize medication-heat interactions as a major public health threat. In 2023, the EPA reported that 92% of heat-related deaths in the U.S. involved people taking at least one medication that interferes with body temperature control. That’s not a coincidence. It’s a pattern.

Research is underway to better understand this. The National Institute on Aging is funding $4.2 million in new studies. Scientists are tracking medication use alongside weather data to build risk models. But that won’t help you tomorrow.

What You Can Do Today

If you or someone you care about takes diuretics or anticholinergics:

• Make a heat safety plan with your doctor.
• Keep a water bottle with you at all times.
• Know your medication names and side effects.
• Use a thermometer in your home. If it’s above 80°F, take action.
• Have a contact who checks on you daily during heat alerts.

Heat doesn’t care if you have a prescription. It only cares if your body can cool down. These medications make that harder. But with the right steps, you can stay safe-even when the weather turns dangerous.