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# Antiparkinson anticholinergics

Central antimuscarinic drugs for tremor and drug-induced dystonia or parkinsonism. Poorly tolerated by older adults: confusion, retention, constipation.

Updated 2026-11-01

## What they are

Trihexyphenidyl, benzatropine and biperiden block muscarinic receptors in the brain. They have modest antiparkinson activity (mostly on tremor and rigidity) and are widely used for acute dystonia and parkinsonism caused by antipsychotics.

## Mechanism of action

In the striatum, dopamine and acetylcholine balance each other. When dopamine falls (Parkinson disease or a dopamine-blocking drug), cholinergic interneurons dominate; blocking their muscarinic receptors restores part of the balance.

Target: Muscarinic acetylcholine receptors

## Key points

- Anticholinergic burden in older adults: confusion, memory loss, delirium, urinary retention, constipation and falls; they are usually avoided in people over 65.
- Contraindicated in angle-closure (narrow-angle) glaucoma.
- They reduce sweating: heat stroke and hyperthermia in hot weather, especially with antipsychotics or tricyclics; paralytic ileus can occur.
- They help acute dystonia and drug-induced parkinsonism but do not help, and can worsen, tardive dyskinesia.
- They are withdrawn gradually: stopping suddenly can worsen parkinsonism.

## Drugs in this class

- [**Benzatropine** A central anticholinergic used for drug-induced dystonia and parkinsonism and for Parkinson tremor. Older adults… Muscarinic acetylcholine receptors (M1 shown)](https://durgical.com/en/pharmacology/benzatropine/)
- [**Trihexyphenidyl** A central anticholinergic for parkinsonian tremor and drug-induced extrapyramidal effects. Avoided in older adults and… Muscarinic acetylcholine receptors (M1 shown)](https://durgical.com/en/pharmacology/trihexyphenidyl/)
- [**Biperiden** A central anticholinergic on the WHO essential list, given by mouth or injection for parkinsonism and acute dystonia… Muscarinic acetylcholine receptors (M1 shown)](https://durgical.com/en/pharmacology/biperiden/)

## Others in the class

- Prociclidina
- Orfenadrina
- Difenhidramina

## Test yourself

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

## Why are antiparkinson anticholinergics usually avoided in older adults?

Older people are more sensitive to their central and peripheral effects: confusion, delirium, urinary retention, constipation and falls.

## Which antipsychotic movement disorder do anticholinergics not treat?

Tardive dyskinesia, which they may even worsen.

## Which eye condition contraindicates them?

Angle-closure glaucoma.

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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. 21 (McGraw Hill, 2023); Farmacología básica y clínica (Katzung), 16.ª ed., cap. 28 (McGraw Hill, 2025); [Trihexyphenidyl: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682160.html) (MedlinePlus (U.S. National Library of Medicine), 2018); [Benztropine: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682155.html) (MedlinePlus (U.S. National Library of Medicine), 2018).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/classes/antiparkinson-anticholinergics/