What is an Anticholinergic? Understanding the Effects of Acetylcholine-Blocking Medications

October 7, 2025 •

5 min read

As many as 20% to 50% of older adults take at least one medication with anticholinergic properties. But what is an anticholinergic and what does it do? These medications work by blocking the action of a key neurotransmitter called acetylcholine, influencing numerous bodily functions from digestion to involuntary muscle movements.

Quick Summary

Anticholinergic medications block the neurotransmitter acetylcholine, affecting involuntary muscle movements and body secretions. They are used for various conditions but come with side effects and specific risks, particularly for older adults.

Key Points

Blocking Acetylcholine: Anticholinergic drugs function by blocking the neurotransmitter acetylcholine, inhibiting signals in both the central and peripheral nervous systems.
Treats Diverse Conditions: This class of medication is used to treat a wide range of health issues, including overactive bladder, COPD, Parkinson's disease, and motion sickness.
Common Side Effects: Due to their widespread effects, anticholinergics can cause common side effects such as dry mouth, constipation, blurred vision, and urinary retention.
Risks for Older Adults: Older adults are particularly vulnerable to adverse effects like confusion, delirium, and cognitive decline, and long-term use may be linked to an increased risk of dementia.
Anticholinergic Burden: The cumulative effect of taking multiple medications with anticholinergic properties, including some antidepressants and antihistamines, can increase the risk of adverse events.
Careful Consideration is Key: Prescribing these medications, especially for older patients, requires a careful evaluation of the benefits versus the risks, often opting for the lowest effective dose for the shortest duration.

The role of acetylcholine

To understand what an anticholinergic does, it's essential to first know the role of acetylcholine (ACh). Acetylcholine is a neurotransmitter, a chemical messenger in the nervous system that transmits signals between nerve cells. It is a critical component of the parasympathetic nervous system, often referred to as the "rest-and-digest" system. The parasympathetic nervous system controls many involuntary bodily functions, including:

Constriction of pupils
Increased secretions (saliva, sweat, tears)
Slowed heart rate
Stimulated digestion and increased gastrointestinal motility
Contraction of the smooth muscle of the bladder wall

Anticholinergic medications interfere with these signals by blocking acetylcholine from binding to its receptors on nerve cells. This inhibition reduces parasympathetic nerve impulses and causes the opposite effects of the neurotransmitter, leading to a wide range of therapeutic benefits—and, in some cases, side effects.

Mechanism of action: Blocking the message

Anticholinergic drugs work by competitively inhibiting the binding of acetylcholine to its receptors. There are two primary types of cholinergic receptors that anticholinergics target: muscarinic and nicotinic. The majority of anticholinergics prescribed are antimuscarinic, meaning they specifically block muscarinic receptors. These are found in the central and peripheral nervous systems, as well as in various organs, including the heart, lungs, and gastrointestinal tract. By blocking these receptors, the drug prevents acetylcholine from carrying out its normal function. The specific effect of the drug depends on which type of receptor it targets and in which area of the body it acts.

For example, to treat an overactive bladder, anticholinergics like oxybutynin block muscarinic receptors in the bladder muscles, which prevents the involuntary contractions that cause frequent urination. For respiratory conditions, such as COPD, inhaled anticholinergics like tiotropium block receptors in the lungs, promoting bronchodilation by relaxing airway muscles. The blocking action can occur in the central nervous system (brain and spinal cord) or the peripheral nervous system (nerves outside the brain and spinal cord), which accounts for the variety of effects and side effects seen with these medications.

Therapeutic uses across various conditions

Anticholinergic medications are a diverse class of drugs used to treat a wide array of medical conditions by targeting specific bodily systems. Some common therapeutic uses include:

Overactive bladder (OAB) and incontinence: By relaxing bladder muscles, anticholinergics reduce urinary urgency and frequency.
Chronic obstructive pulmonary disease (COPD) and asthma: Inhaled anticholinergics help open airways by relaxing the muscles around the bronchioles.
Parkinson's disease: These drugs can help manage tremors and other involuntary muscle movements, especially in younger patients.
Gastrointestinal disorders: Conditions like irritable bowel syndrome (IBS) can be managed by anticholinergics that decrease muscle spasms and motility in the gut.
Motion sickness: Scopolamine, an anticholinergic, is highly effective for preventing nausea and vomiting associated with motion sickness.
Insomnia: Certain antihistamines with anticholinergic effects, such as diphenhydramine, are used as sleep aids.
Excessive sweating (hyperhidrosis): Medications like glycopyrrolate are used to reduce sweat gland secretions.
Certain types of poisoning: Atropine is used as an antidote for poisoning from organophosphate insecticides or nerve gas, which overstimulate the cholinergic system.

Notable side effects and toxicity

Because acetylcholine is involved in so many bodily functions, blocking its action can lead to a variety of side effects. Many of the common side effects are memorably summarized by the classic mnemonic: "Can't see, can't pee, can't spit, can't poop".

Common peripheral side effects:

Dry mouth (Can't spit): Decreased salivary secretions.
Blurred vision (Can't see): Due to pupil dilation and the eye's inability to focus properly.
Urinary retention (Can't pee): Difficulty emptying the bladder due to a relaxed bladder muscle.
Constipation (Can't poop): Slowed motility of the gastrointestinal tract.
Decreased sweating: Can increase body temperature, raising the risk of heat exhaustion.
Tachycardia: An increase in heart rate.

Central nervous system (CNS) side effects:

Confusion and delirium: Affects memory, learning, and overall cognitive function.
Drowsiness or sedation: Can impair alertness and coordination.
Hallucinations: Can occur, particularly in older adults and at higher doses.

In severe cases, an accumulation of anticholinergic agents can lead to anticholinergic toxicity or syndrome, which requires immediate medical attention. The mnemonic "Hot as a hare, dry as a bone, red as a beet, mad as a hatter" describes the hallmark signs: fever, dry skin, flushed skin, and confusion or delirium.

Anticholinergics and older adults: A crucial consideration

Older adults are especially susceptible to the adverse effects of anticholinergic medications for several reasons. As a person ages, their body's natural production of acetylcholine decreases, making them more sensitive to drugs that further block its effects. Additionally, older individuals often take multiple medications for various conditions, which can lead to a cumulative effect known as "anticholinergic burden". This cumulative effect increases the risk of serious side effects, including falls, delirium, and cognitive decline.

Recent studies have shown a link between long-term use of certain potent anticholinergics and an increased risk of dementia. Healthcare providers use tools like the Beers Criteria, a list of potentially inappropriate medications for older adults, to guide prescribing decisions. For older patients, the benefits of an anticholinergic must be carefully weighed against the risks, and safer alternatives or the lowest effective dose for the shortest possible duration should be considered.

Anticholinergic drugs versus cholinergic drugs: A comparison

Anticholinergic and cholinergic drugs have opposite effects because they interact with acetylcholine receptors in contrasting ways. The following table highlights their key differences in mechanism and physiological impact.


Feature	Anticholinergic Drugs	Cholinergic Drugs
Mechanism of Action	Blocks acetylcholine from binding to its receptors.	Enhances or mimics the action of acetylcholine.
Effect on Parasympathetic Nervous System	Inhibits the "rest-and-digest" system.	Stimulates the "rest-and-digest" system.
Pupils	Dilates pupils (mydriasis).	Constricts pupils.
Heart Rate	Increases heart rate (tachycardia).	Decreases heart rate.
Secretions (Saliva, Tears, Sweat)	Decreases secretions, leading to dry mouth and eyes.	Increases secretions.
Gastrointestinal Motility	Decreases motility, causing constipation.	Increases motility.
Bladder Muscle	Relaxes bladder muscle, leading to urinary retention.	Contracts bladder muscle, stimulating urination.
Common Therapeutic Use	Overactive bladder, COPD, Parkinson's disease.	Alzheimer's disease, glaucoma, myasthenia gravis.

Conclusion: Balancing benefits and risks

Anticholinergic medications are a powerful and widely used class of drugs that provide significant benefits for a range of conditions by blocking the effects of the neurotransmitter acetylcholine. From treating chronic respiratory issues and urinary incontinence to managing symptoms of Parkinson's disease, their therapeutic applications are diverse. However, the widespread nature of acetylcholine in the body means that these medications can also produce a variety of side effects, particularly in older adults, who are at a higher risk of cognitive and functional decline. The cumulative effect of multiple drugs with anticholinergic properties can pose a significant health risk. Therefore, it is essential for healthcare providers and patients to carefully weigh the benefits against the risks, monitor for potential side effects, and consider safer alternatives, especially in older and more vulnerable populations. The decision to use an anticholinergic should always be made in consultation with a medical professional. For more information, the Verywell Health article "Decoding Anticholinergic Drugs: Uses, Safety, and More" provides additional details on this important topic.

Frequently Asked Questions

The primary function of an anticholinergic drug is to block the action of a neurotransmitter called acetylcholine (ACh). By blocking ACh from binding to its receptors, these drugs reduce or inhibit nerve impulses that control involuntary muscle movements and bodily secretions.

Examples of anticholinergics include oxybutynin (used for overactive bladder), tiotropium (for COPD), and scopolamine (for motion sickness). Many other medications, like some antihistamines (e.g., diphenhydramine) and tricyclic antidepressants, also have anticholinergic effects.

Anticholinergic burden refers to the cumulative effect of a patient taking multiple medications that have anticholinergic properties. Since many common drugs carry these effects, taking several can lead to a magnified risk of adverse side effects, especially in older adults.

Older adults are more sensitive to anticholinergic effects because their bodies produce less acetylcholine naturally, and their ability to clear drugs from their system is slower. This increases the risk of side effects like cognitive impairment, falls, and delirium.

Yes, anticholinergics can affect memory, particularly in older adults. By blocking acetylcholine in the brain, they can cause confusion, memory problems, and a higher risk of cognitive decline, especially with long-term use.

Anticholinergic toxicity occurs when a dangerous level of anticholinergic agents accumulates in the body. Symptoms can be severe and include high fever, dry and flushed skin, dilated pupils, agitation, delirium, and rapid heart rate.

Certain anticholinergics, such as scopolamine, are effective for motion sickness by blocking acetylcholine receptors in the central nervous system and the vestibular system (which controls balance), helping to prevent nausea and vomiting.