What drugs block the parasympathetic nervous system? An overview of anticholinergics

October 6, 2025 •

4 min read

Affecting involuntary bodily functions, the parasympathetic nervous system is responsible for the 'rest and digest' response. When these functions need to be reduced for therapeutic purposes, doctors can prescribe specific medications. What drugs block the parasympathetic nervous system? Known as anticholinergics, these medications inhibit the neurotransmitter acetylcholine, thereby decreasing parasympathetic activity for targeted effects.

Quick Summary

Anticholinergics, or parasympatholytic drugs, block the neurotransmitter acetylcholine to inhibit the parasympathetic nervous system. This article details the different types of anticholinergic drugs, their mechanisms of action, and their wide range of clinical applications for treating conditions like COPD, overactive bladder, and Parkinson's symptoms.

Key Points

Anticholinergics are parasympathetic blockers: This class of drugs, also known as parasympatholytics, inhibits the action of acetylcholine, the primary neurotransmitter of the parasympathetic nervous system.
Two main types of anticholinergic receptors: Anticholinergic drugs block either muscarinic receptors (on effector organs) or nicotinic receptors (at autonomic ganglia and neuromuscular junctions).
Antimuscarinic drugs have broad applications: These agents are used for treating overactive bladder (oxybutynin), COPD (ipratropium), motion sickness (scopolamine), and certain symptoms of Parkinson's disease (benztropine).
Antinicotinic drugs are mainly for muscle paralysis: Neuromuscular blockers like vecuronium, which act at nicotinic receptors, are primarily used in anesthesia to relax muscles during surgery.
Side effects are widespread due to systemic action: Common side effects result from inhibiting 'rest and digest' functions and include dry mouth, blurred vision, constipation, urinary retention, and, particularly in the elderly, cognitive issues.
Careful consideration is required for elderly patients: Older adults are more vulnerable to the adverse effects of anticholinergics, such as confusion and delirium, and should be monitored closely.

The nervous system regulates every involuntary bodily function, from heartbeat and digestion to gland secretion. This regulation is managed by the autonomic nervous system, which is divided into the sympathetic ('fight or flight') and parasympathetic ('rest and digest') branches. When the body's parasympathetic activity becomes overactive or needs to be suppressed for treatment, medications known as anticholinergics are used to block its effects. These drugs, also called parasympatholytics, act by inhibiting the neurotransmitter acetylcholine (ACh) at its receptor sites.

The Role of Acetylcholine and Its Receptors

Acetylcholine is the primary chemical messenger that transmits signals within the parasympathetic nervous system. It binds to two main types of cholinergic receptors: muscarinic and nicotinic. The specific effects of ACh binding depend on the receptor type and location. By blocking these receptors, anticholinergic drugs disrupt the signal, preventing the characteristic parasympathetic response. The therapeutic goal of using these blockers is to achieve a controlled inhibition of parasympathetic activity in specific organs while minimizing unintended side effects.

Antimuscarinic Agents

The majority of parasympathetic blocking drugs are antimuscarinic agents. They work by competing with acetylcholine for binding sites on muscarinic receptors located in the brain, heart, eyes, smooth muscles, and glands. These receptors are responsible for mediating many 'rest and digest' functions. Antimuscarinics can be non-selective or selectively target certain receptor subtypes to produce specific therapeutic effects. Notable examples include:

Atropine: A naturally occurring belladonna alkaloid, atropine is a non-selective muscarinic antagonist used to treat symptomatic bradycardia (slow heart rate), as an antidote for cholinergic poisoning, and to cause pupil dilation for eye examinations.
Scopolamine: Also a belladonna alkaloid, scopolamine is primarily used to prevent motion sickness and to treat postoperative nausea and vomiting, often administered via a transdermal patch. It readily crosses the blood-brain barrier.
Ipratropium and Tiotropium: These are inhaled antimuscarinics used to treat respiratory conditions like chronic obstructive pulmonary disease (COPD) and asthma by causing bronchodilation. They act locally in the airways, limiting systemic side effects.
Oxybutynin, Tolterodine, and Solifenacin: Used to treat overactive bladder (OAB) and urinary incontinence, these agents work by relaxing the smooth muscles of the bladder detrusor muscle.
Benztropine and Trihexyphenidyl: These centrally acting antimuscarinics are used to treat the symptoms of Parkinson's disease, particularly tremors and rigidity.

Antinicotinic Agents

Another class of anticholinergic drugs, antinicotinic agents, blocks acetylcholine at nicotinic receptors. These are primarily used in anesthesia to induce muscle paralysis, but some affect the autonomic ganglia. The two main categories are:

Neuromuscular Blockers: Drugs like vecuronium, atracurium, and pancuronium block nicotinic receptors at the neuromuscular junction, preventing muscle contraction. They are crucial for muscle relaxation during surgical procedures.
Ganglionic Blockers: While less common in modern therapeutics, drugs like mecamylamine block nicotinic receptors in the autonomic ganglia, affecting both sympathetic and parasympathetic nervous systems.

Clinical Applications of Parasympathetic Blockers

Parasympatholytics are used to treat a diverse range of medical conditions by targeting specific organ systems:

Respiratory Disorders: By blocking muscarinic receptors in the airways, drugs like ipratropium cause bronchodilation, which is highly beneficial for patients with COPD and asthma.
Overactive Bladder: Antimuscarinics such as oxybutynin, solifenacin, and tolterodine are used to decrease bladder contractions, treating urgency, frequency, and incontinence.
Gastrointestinal Disorders: These drugs can reduce motility and secretion in the GI tract. Hyoscyamine and dicyclomine are used to treat irritable bowel syndrome (IBS) and other colicky abdominal pains.
Neurological Conditions: In Parkinson's disease, central muscarinic blockers help to reduce tremors. Scopolamine is effective against motion sickness by acting on the central nervous system to reduce nausea and vomiting.
Cardiovascular Conditions: Atropine is used in emergencies to treat symptomatic bradycardia by blocking vagal (parasympathetic) nerve effects on the heart.
Ophthalmology: Atropine and cyclopentolate are used to dilate pupils (mydriasis) for eye examinations and to treat certain eye conditions by relaxing the ciliary muscles (cycloplegia).

Comparison of Antimuscarinic and Antinicotinic Blockers


Feature	Antimuscarinic Blockers	Antinicotinic Blockers
Mechanism	Competitively block muscarinic receptors.	Block nicotinic receptors.
Primary Location of Action	Postganglionic parasympathetic nerve endings on effector organs.	Neuromuscular junctions (muscle type) and autonomic ganglia (ganglion type).
Key Examples	Atropine, scopolamine, ipratropium, oxybutynin.	Vecuronium, atracurium (neuromuscular blockers), mecamylamine (ganglionic blocker).
Therapeutic Uses	Treat bradycardia, motion sickness, COPD, overactive bladder, Parkinson's symptoms.	Used as muscle relaxants during surgery, some investigational uses.
Clinical Effects	Increased heart rate, bronchodilation, decreased GI motility, urinary retention, pupil dilation.	Muscle paralysis (neuromuscular blockers), systemic effects on blood pressure (ganglionic blockers).

Common Side Effects and Risks

By blocking parasympathetic activity, these drugs cause predictable and widespread side effects related to the inhibited 'rest and digest' functions. Common anticholinergic side effects include:

Dry Mouth: Decreased salivation.
Blurred Vision: Due to pupil dilation and the inability to focus on near objects.
Constipation: Decreased gastrointestinal motility.
Urinary Retention: Difficulty or inability to empty the bladder.
Drowsiness and Sedation: Especially with drugs that cross the blood-brain barrier like scopolamine.
Confusion and Memory Problems: Older patients are particularly susceptible to central nervous system effects, and prolonged use can increase the risk of cognitive decline.

Contraindications for these drugs include narrow-angle glaucoma, benign prostatic hyperplasia with urinary retention, and significant heart disease. The specific contraindications depend on the drug and the patient's overall health.

Conclusion

Drugs that block the parasympathetic nervous system, predominantly anticholinergics, are an important class of medications with a wide array of therapeutic uses. By targeting muscarinic and nicotinic acetylcholine receptors, these drugs can treat conditions ranging from respiratory disorders and overactive bladder to motion sickness and Parkinson's symptoms. However, their action on the 'rest and digest' system can lead to various systemic side effects, requiring careful management, especially in vulnerable populations like the elderly. Understanding the specific mechanism of different parasympathetic blockers is crucial for optimizing their therapeutic benefits while minimizing adverse effects.

Anticholinergic Medications - StatPearls - NCBI Bookshelf

Frequently Asked Questions

The primary mechanism of these drugs, called anticholinergics, is to block the action of the neurotransmitter acetylcholine (ACh) at its receptor sites, which inhibits the signals of the parasympathetic nervous system.

Antimuscarinic drugs are used for a variety of conditions, including respiratory disorders like COPD and asthma (ipratropium, tiotropium), overactive bladder (oxybutynin, solifenacin), motion sickness (scopolamine), and Parkinson's disease tremors (benztropine).

Anticholinergic drugs, like atropine, can block the vagal (parasympathetic) nerve's slowing effect on the heart, leading to an increased heart rate. This is why atropine is used to treat symptomatic bradycardia (slow heartbeat).

Dry mouth occurs because these drugs inhibit secretions from the salivary glands, and blurred vision results from their effect on the eyes, causing pupil dilation and paralyzing the ciliary muscle that controls focus.

Elderly individuals are at a higher risk for adverse effects, including confusion, cognitive decline, delirium, and impaired homeostatic regulation. These effects are due to decreased cholinergic reserve and altered metabolism in older adults.

Antimuscarinic drugs primarily block muscarinic receptors on effector organs, while antinicotinic drugs block nicotinic receptors, mainly at the neuromuscular junction or autonomic ganglia. Antimuscarinics have more widespread therapeutic uses, while antinicotinics are often used for muscle relaxation during surgery.

Yes, some over-the-counter medications, particularly older antihistamines like diphenhydramine, have anticholinergic properties that can cause side effects such as drowsiness and dry mouth.