Heat Exposure Precautions with Diuretics and Anticholinergics

When the temperature climbs above 85°F, 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’s dangerous. These common medications, prescribed for conditions like high blood pressure, heart failure, overactive bladder, and depression, can silently disable your body’s ability to cool itself. And when summer heat hits, that’s when the real risk starts.

How Diuretics Put You at Risk in the Heat

Diuretics-often called water pills-help your body get rid of extra fluid. That’s great for lowering blood pressure or reducing swelling from heart failure. But in hot weather, they work against you. Medications like furosemide (Lasix), hydrochlorothiazide (Microzide), and chlorthalidone (Hygroton) make you pee more. That sounds harmless until you realize your body is losing fluids you can’t afford to lose when you’re sweating.

When it’s hot, your body naturally sweats to cool down. But if you’re on a diuretic, your kidneys are already pushing out water and salt. The result? Lower blood volume, thicker blood, and less ability to deliver heat away from your core. You might not feel thirsty until you’re already dehydrated. And by then, your heart is working harder, your electrolytes are out of balance, and your body can’t keep up.

Studies show people taking loop diuretics like furosemide have a 37% higher chance of being hospitalized for heat illness during summer months-even when temperatures are only in the low 80s. That’s not a heatwave. That’s a normal July day in Toronto. And it’s enough to push someone on diuretics into danger.

Anticholinergics: The Silent Killer in the Heat

Anticholinergics are even more dangerous in heat because they don’t just affect fluid balance-they stop sweating entirely. Medications like oxybutynin (Ditropan) for overactive bladder, tolterodine (Detrol), and tricyclic antidepressants like amitriptyline (Elavil) block acetylcholine, a chemical your body uses to trigger sweat glands.

Without sweat, your body has no way to cool down. Research shows people on high-burden anticholinergic drugs (ACB score of 3) lose 30-50% of their sweating capacity. That means even if you’re outside in 90°F weather, your skin stays dry. Your core temperature keeps rising. You don’t feel hot because your body can’t signal it. You might just feel dizzy, confused, or tired-symptoms that look like aging or side effects of the drug itself.

This is why so many older adults die in heatwaves. In Oregon’s 2021 heat dome, 63% of the people who died from heat exposure were taking either a diuretic or an anticholinergic. Many weren’t even aware their meds were making them vulnerable. They thought they were just getting older.

Why You Can’t Just Drink More Water

It’s tempting to say, “Just drink more water.” But that’s not enough-and sometimes, it’s risky.

People with heart failure are often told to limit fluids to avoid fluid overload. But in extreme heat, that advice can be deadly. The CDC says it’s okay to temporarily relax fluid restrictions during heat events if you’re on diuretics. Your doctor might even adjust your dose. But you don’t get to decide that yourself.

Drinking too much water without replacing lost salt can also cause hyponatremia-dangerously low sodium levels. That can lead to seizures, brain swelling, or even death. So it’s not about drinking more. It’s about drinking smart, and knowing when your body needs help.

What You Should Do Right Now

If you or someone you care for takes diuretics or anticholinergics, here’s what to do:

1. Check your meds. Look up your medications on the Anticholinergic Burden Scale (ACB). If any have a score of 3, you’re at high risk. Common ones: oxybutynin, tolterodine, diphenhydramine (Benadryl), amitriptyline, and some antipsychotics.
2. Don’t skip your meds. Stopping them without talking to your doctor can cause blood pressure spikes, heart rhythm problems, or bladder accidents. Risk from the drug isn’t worth the risk of stopping it.
3. Ask your doctor about dose changes. During heatwaves, your doctor might lower your diuretic dose for a few days. That’s not unusual. In one study, 42% of heart failure patients on diuretics needed temporary dose adjustments during a summer heatwave.
4. Wear the right clothes. Light-colored, loose, breathable fabrics help even if you’re not sweating much. Avoid dark colors-they absorb heat. Hats and sunglasses help too.
5. Use sunscreen. Many anticholinergics make your skin more sensitive to the sun. Sunburn adds stress to your body and raises your core temperature faster.
6. Set up a check-in system. If you’re over 65 or have memory issues, have someone call or visit you twice a day during hot weather. Heat confusion can make you forget you’re in danger. You might not realize you need help until it’s too late.

Recognizing the Warning Signs

Heat illness doesn’t always look like classic heatstroke. With these meds, symptoms are subtle and easy to miss:

• Feeling unusually tired or weak
• Headache that won’t go away
• Dizziness or lightheadedness when standing
• Confusion, slurred speech, or trouble remembering things
• Dry skin-even in hot weather
• Fast heartbeat or chest discomfort
• Nausea or vomiting

If you notice any of these, get indoors, cool down, and call your doctor. Don’t wait for a fever or collapse. By then, it’s too late.

What Your Doctor Should Be Doing

Doctors aren’t always trained to ask about heat risks. But they should. If you’re on one of these meds, your doctor should:

• Review your meds every spring before heat season starts
• Discuss your heat exposure habits (do you walk outside? Do you have AC?)
• Provide a written plan: what to do if it gets hot, when to call for help, and whether to adjust your dose
• Know your other meds-some drugs, like beta-blockers or SSRIs, add to the risk

Don’t assume your doctor knows. Bring up heat safety like you would any other side effect. It’s part of your care.

The Bigger Picture

This isn’t just about individual choices. Climate change is making heatwaves more frequent, longer, and deadlier. In the U.S., the number of days over 90°F has increased by 47% since 1970. Older adults on these meds are among the most vulnerable. Yet, there’s still no national system that tracks who’s at risk.

The CDC’s Heat and Health Tracking System now covers 25 states and is starting to include medication data. That’s a start. But until we have better research-especially on older adults with multiple chronic conditions-we’re flying blind.

Right now, the best defense is knowledge. Know your meds. Know your risk. Know what to do. And don’t let silence be your downfall. Heat doesn’t care if you’re taking a pill for your heart, your bladder, or your mood. It only cares if your body can cool down.

Ask your doctor today: “Could my medications make me more vulnerable to heat?” That one question could save your life.