Anticholinergic Drugs: What They Are, How They Work, and What You Need to Know

When you take a medication that blocks anticholinergic, a class of drugs that inhibit the neurotransmitter acetylcholine to reduce muscle spasms, secretions, or nerve signals. Also known as cholinergic blockers, these drugs are used for everything from allergies to overactive bladder—but they don’t come without trade-offs. Acetylcholine helps your brain, heart, lungs, and digestive system function normally. When anticholinergics shut it down, symptoms like sneezing or cramping may improve, but so do memory, focus, and even your ability to move comfortably at night.

Many people don’t realize that common over-the-counter antihistamines, like diphenhydramine in Benadryl, are also anticholinergic drugs. They help with runny noses, but they also slow down brain activity, which is why they make you drowsy—and why they can make restless legs syndrome, a condition where legs feel uncomfortable and urge you to move, especially at night much worse. Studies show these drugs block dopamine pathways in the brain, which directly fuels the burning, crawling feeling in your limbs. If you’ve been taking Benadryl for sleep and your legs won’t stop twitching, this might be why.

Anticholinergics show up in more places than you think: asthma inhalers, motion sickness pills, even some antidepressants and Parkinson’s meds. The problem isn’t that they’re bad—they’re useful when prescribed correctly. But when used long-term, especially in older adults, they’re linked to higher risks of dementia, urinary retention, constipation, and blurred vision. And because they’re often taken without a doctor’s oversight, many people don’t connect their memory lapses or dry mouth to the meds they’ve been popping for years.

What you’ll find here isn’t a list of every anticholinergic drug ever made. It’s a practical look at the ones you’re likely already using, the hidden risks you might not know about, and what you can switch to instead. We’ve pulled together real comparisons from posts about allergy meds that worsen restless legs, how generic drugs can carry the same risks as brand names, and why inactive ingredients sometimes matter more than you’d guess. You’ll see how drugs like Allegra and Zyrtec stack up against Benadryl, why some people get away with anticholinergics while others don’t, and what to ask your pharmacist before the next refill.