Anticholinergic drugs are medications that block a chemical messenger called acetylcholine from reaching its receptors throughout your body. Acetylcholine controls a wide range of functions, from muscle contractions and heart rate to saliva production and bladder control, so blocking it produces effects across many organ systems. Some medications are designed specifically to block acetylcholine, while others do so as an unintended side effect.
How Anticholinergic Drugs Work
Acetylcholine acts on two types of receptors: muscarinic and nicotinic. Anticholinergic drugs almost exclusively target muscarinic receptors, which are concentrated in the brain, the organs controlled by your autonomic nervous system (heart, lungs, gut, bladder), and glands like those that produce saliva and sweat. When a drug blocks these receptors, the organ or gland that normally responds to acetylcholine can no longer get the signal to act.
The specific effect depends on where in the body the blocking happens. In the bladder, acetylcholine normally triggers the muscle to contract so you can urinate. Block that signal, and the bladder relaxes. In the airways, acetylcholine causes the muscles around your bronchial tubes to tighten. Block that, and the airways open up. This is why the same class of drug can treat conditions as different as overactive bladder and COPD.
Conditions They Treat
Because acetylcholine is involved in so many body functions, anticholinergic drugs are prescribed for a surprisingly wide range of conditions:
- Overactive bladder and urge incontinence: Oxybutynin, solifenacin, and tolterodine reduce bladder spasms and the constant urge to urinate.
- COPD and asthma: Ipratropium and tiotropium relax airway muscles to make breathing easier.
- Parkinson’s disease: Benztropine and trihexyphenidyl help control tremors and muscle stiffness.
- Motion sickness: Scopolamine prevents nausea and vomiting during travel.
- Slow heart rate: Atropine speeds up the heart when it beats too slowly.
- Excessive drooling or sweating: Glycopyrrolate reduces saliva production, and topical oxybutynin can treat excessive sweating.
Drugs With Hidden Anticholinergic Effects
Many common medications were not designed as anticholinergics but block acetylcholine as a side effect. This is an important distinction because people often take these drugs without realizing they carry anticholinergic risks. The most common culprits include tricyclic antidepressants (like amitriptyline), older antihistamines (like diphenhydramine, the active ingredient in many over-the-counter sleep aids and allergy medications), and some antipsychotic medications used for bipolar disorder or schizophrenia.
Diphenhydramine deserves special mention because it is so widely available. It is the main ingredient in products marketed for sleep and allergies, and many people take it regularly without a prescription. It carries the same anticholinergic burden as drugs prescribed specifically for that purpose.
Common Side Effects
The side effects of anticholinergic drugs are predictable once you understand what acetylcholine normally does. Medical students learn them through a memorable set of phrases: “dry as a bone” (reduced sweating and dry mouth), “blind as a bat” (blurred vision and dilated pupils), “hot as a hare” (fever from the inability to sweat and cool down), “red as a beet” (flushed skin from dilated blood vessels), “mad as a hatter” (confusion and delirium), “bloated as a toad” (constipation from slowed gut movement), and “full as a flask” (urinary retention from an inability to contract the bladder).
Not everyone experiences all of these, and severity depends on the dose, the specific drug, and individual sensitivity. The most frequently reported side effects at typical doses are dry mouth, constipation, blurred vision, drowsiness, and difficulty urinating. In the brain, these drugs can cause dizziness, sedation, and cognitive sluggishness, particularly in older adults.
Long-Term Risk: Dementia
The most concerning finding about anticholinergic drugs in recent years is their association with dementia. A landmark study published in JAMA Internal Medicine tracked older adults over 10 years and found a clear dose-response relationship: the more anticholinergic medication someone had taken over time, the higher their risk of developing dementia.
People with the highest cumulative exposure (equivalent to taking a strong anticholinergic daily for more than three years) had a 54% increased risk of dementia and a 63% increased risk of Alzheimer’s disease compared to people who had not used these drugs. Moderate exposure (one to three years of daily use) showed a smaller, 23% increase in dementia risk. Short-term use of less than three months did not show a statistically significant increase.
This does not mean that everyone who takes an anticholinergic will develop dementia. It means that cumulative, long-term use raises the probability, and the risk increases with total lifetime exposure. This is especially relevant for people who take multiple medications with anticholinergic effects at the same time, or who have been on one for years.
Anticholinergic Burden: Why Stacking Matters
Researchers developed a tool called the Anticholinergic Cognitive Burden (ACB) scale to measure how much anticholinergic activity a person’s total medication list produces. Each drug is scored from 1 to 3. A score of 1 means the drug has mild anticholinergic properties detectable in lab studies. A score of 2 means it has clinically noticeable anticholinergic effects. A score of 3 means the drug is potent enough to potentially cause delirium on its own.
Your total score is the sum of all your medications’ individual scores. Someone taking a mild antihistamine (score of 1) alongside a bladder medication (score of 3) and a tricyclic antidepressant (score of 3) could have a combined burden of 7, placing them at significant risk for cognitive side effects. This stacking effect is why it matters to look at your full medication list rather than evaluating each drug in isolation. A pharmacist can help calculate your total anticholinergic burden.
Reducing Your Anticholinergic Exposure
For many conditions treated with anticholinergic drugs, alternatives exist. For allergies, newer antihistamines like cetirizine, loratadine, and fexofenadine have far less anticholinergic activity than older options like diphenhydramine. For sleep, the habitual use of diphenhydramine-based sleep aids is one of the most common sources of unnecessary anticholinergic exposure.
For overactive bladder, non-drug approaches can be effective either alone or alongside reduced medication. Bladder training involves gradually increasing the time between bathroom trips to retrain the bladder’s capacity. Pelvic floor muscle exercises strengthen the muscles that control urination. Behavioral therapy combines these techniques with biofeedback to help you develop better bladder control. For people who do not respond to conservative measures, nerve stimulation techniques and botulinum toxin injections into the bladder wall offer options that avoid daily anticholinergic medication entirely.
If you are taking one or more anticholinergic medications, the practical step is to have your full medication list reviewed. The goal is not necessarily to stop all anticholinergic drugs, since some conditions genuinely require them, but to identify cases where a lower-risk alternative would work just as well and to eliminate unnecessary overlap where multiple drugs are contributing anticholinergic effects you did not know about.