Anticholinergic drugs are a class of medications that block the neurotransmitter acetylcholine from binding to receptors in the nervous system.
By inhibiting these signals, they block the parasympathetic nervous system, known as (the “rest and digest” system), which treats conditions like overactive bladder, COPD, Parkinson’s disease, and allergies, but often causes side effects like dry mouth and constipation.
Acetylcholine is a chemical messenger in the body that activates involuntary muscle movements, glands, and the “rest-and-digest” processes of the autonomic nervous system.
Anticholinergics jam these signals to produce a variety of targeted therapeutic effects.
Urinary Incontinence & Overactive Bladder: Blocks involuntary bladder contractions.
Examples: Oxybutynin (Ditropan, Oxytrol), Tolterodine (Detrol), Solifenacin (Vesicare).
COPD & Asthma: Relaxes airway muscles and reduces mucus production.
Examples: Ipratropium (Atrovent), Tiotropium (Spiriva).
Allergies & Motion Sickness: Blocks histamine and prevents nausea/vomiting pathways.
Examples: Diphenhydramine (Benadryl), Dimenhydrinate (Dramamine), Scopolamine.
Parkinson’s Disease: Used to reduce tremors and muscle stiffness. Examples: Benztropine (Cogentin), Trihexyphenidyl.
Gastrointestinal Disorders: Relaxes smooth muscles in the GI tract to stop spasms and diarrhea.
Hyoscyamine (Levsin), Dicyclomine (Bentyl).
Side Effects
Anticholinergic drugs broadly block involuntary functions, they are famous for an array of classic peripheral side effects, commonly summarized by the medical mnemonic: “Blind as a bat, mad as a hatter, red as a beet, hot as a hare, dry as a bone.”
Common: Dry mouth, dry eyes, blurred vision, constipation, and difficulty urinating.
Severe (often in high doses or elderly patients): Confusion, memory issues, hallucinations, and rapid heart rate (tachycardia).
Many over-the-counter (OTC) drugs—such as first-generation antihistamines, certain antidepressants, and sleep aids—have strong anticholinergic properties.
Taking multiple medications with these properties has a cumulative effect known as the anticholinergic burden.
In older adults, chronic, heavy anticholinergic burden is heavily associated with a higher risk of cognitive decline, falls, and dementia.
Anticholinergic burden is the cumulative effect of taking one or more medications with anticholinergic properties — drugs that block acetylcholine receptors.
Many common medications have this effect even when it’s not their main purpose: certain antihistamines (diphenhydramine), tricyclic antidepressants, bladder antispasmodics (oxybutynin), some antipsychotics, and drugs for COPD or Parkinson’s.
Short-term: dry mouth, blurred vision, constipation, urinary retention, confusion
Higher burden, especially in older adults: increased fall risk, cognitive impairment, and some studies link long-term high burden to elevated dementia risk
Effects are cumulative — several mildly anticholinergic drugs together can add up to a significant burden even if no single one seems risky
Clinicians often use scoring tools like the Anticholinergic Cognitive Burden (ACB) Scale or Anticholinergic Risk Scale, which rate individual drugs (0–3) and sum them across a person’s medication list.
A total score of 3+ is generally considered clinically significant.