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[Pharmacology](https://durgical.com/en/pharmacology/) · Class

# Antimuscarinics (anticholinergics)

Drugs that block acetylcholine at muscarinic receptors: they dry secretions, speed the heart, relax the gut and bladder and widen the pupils.

Updated 2026-11-01

## What they are

Competitive blockers of the five muscarinic receptor subtypes (M1 to M5; see the topic «Autonomic receptor subtypes»). The natural belladonna alkaloids atropine and scopolamine (hyoscine) are tertiary amines that enter the brain; quaternary drugs such as hyoscine butylbromide and glycopyrronium stay outside it and are poorly absorbed by mouth. Uses include bradycardia, organophosphate poisoning, secretions in anaesthesia and palliative care, intestinal cramps, motion sickness, the eye exam, COPD (inhaled agents) and overactive bladder (a class of its own here).

## Mechanism of action

They sit in the acetylcholine pocket of the muscarinic receptor without activating it. The block is competitive, so a large excess of acetylcholine (for example after a cholinesterase inhibitor) can overcome it. Most drugs hardly distinguish between subtypes, so one wanted effect comes with the rest: dry mouth, blurred near vision, fast heart rate, constipation, urinary retention, less sweating and, with tertiary drugs, confusion.

Target: Muscarinic acetylcholine receptors M1 to M5

## Key points

- Anticholinergic toxidrome: hot, dry, flushed skin; dilated pupils; fast heart; urinary retention; silent bowel; agitated delirium. Dry skin separates it from sympathomimetic poisoning, which sweats.
- Organophosphate poisoning: atropine is repeated until bronchial secretions dry, but it does not reverse muscle weakness; that needs pralidoxime, given early, plus airway support.
- Tertiary (atropine, scopolamine) cross into the brain; quaternary (hyoscine butylbromide, glycopyrronium) do not, so they cause less confusion.
- Angle-closure glaucoma, urinary retention and bowel obstruction are the classic reasons not to give them; older adults are prone to confusion and falls.
- Many other drugs have anticholinergic effects: tricyclic antidepressants, first-generation antihistamines and phenothiazines add to this class.

## Drugs in this class

- [**Atropine** The classic muscarinic blocker: it speeds a slow heart, dries secretions and is the key antidote for organophosphate… Muscarinic acetylcholine receptors (M1 to M5)](https://durgical.com/en/pharmacology/atropine/)
- [**Hyoscine butylbromide** A gut antispasmodic widely used in Colombia for cramping abdominal pain. It is a quaternary drug that does not enter… Muscarinic acetylcholine receptors of smooth muscle (mainly M3)](https://durgical.com/en/pharmacology/hyoscine-butylbromide/)
- [**Hyoscine hydrobromide (scopolamine)** A belladonna alkaloid that enters the brain; a skin patch prevents motion sickness. In Colombia it is also known for… Muscarinic acetylcholine receptors (M1 to M5)](https://durgical.com/en/pharmacology/hyoscine-hydrobromide/)
- [**Glycopyrronium** A quaternary antimuscarinic used in anaesthesia to dry secretions and to block the slow heart rate caused by… Muscarinic acetylcholine receptors (M1 to M5)](https://durgical.com/en/pharmacology/glycopyrronium/)
- [**Dicycloverine** An oral antispasmodic for the cramping pain of irritable bowel syndrome. It blocks muscarinic receptors and relaxes… Muscarinic acetylcholine receptors of gut smooth muscle](https://durgical.com/en/pharmacology/dicycloverine/)

## Others in the class

- Ipratropium and tiotropium (inhaled)
- Tropicamide and cyclopentolate (eye drops)
- Hyoscyamine
- Benztropine and trihexyphenidyl (Parkinson disease)

## Test yourself

Think of the answer, then tap the question to see it.

## Which single sign best separates anticholinergic poisoning from sympathomimetic (for example cocaine) poisoning?

The skin: dry in anticholinergic poisoning, sweaty in sympathomimetic poisoning. Both cause fast heart rate and dilated pupils.

## In organophosphate poisoning, what does atropine treat and what does it not?

It treats the muscarinic effects (secretions, bronchospasm, bradycardia) but not the nicotinic muscle weakness and paralysis.

## Why does glycopyrronium cause less confusion than atropine?

It is a quaternary amine and barely crosses the blood-brain barrier.

## Which eye condition is the classic contraindication to antimuscarinics?

Angle-closure (narrow-angle) glaucoma: pupil dilation can block drainage and trigger an acute attack.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 11 (McGraw Hill, 2023); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 12 (McGraw Hill, 2023); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=A03B) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025).

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Representative model, for educational purposes only.

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