[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Antiparkinson anticholinergics](https://durgical.com/en/pharmacology/classes/antiparkinson-anticholinergics/) › Trihexyphenidyl [Pharmacology](https://durgical.com/en/pharmacology/) · [Antiparkinson anticholinergics](https://durgical.com/en/pharmacology/classes/antiparkinson-anticholinergics/) # Trihexyphenidyl A central anticholinergic for parkinsonian tremor and drug-induced extrapyramidal effects. Avoided in older adults and narrow-angle glaucoma. Updated 2026-11-01 - Class: [Antiparkinson anticholinergics](https://durgical.com/en/pharmacology/classes/antiparkinson-anticholinergics/) - Receptor: Muscarinic acetylcholine receptors (M1 shown) - ATC code: N04AA01 Also called: Benzhexol ◎**Muscarinic acetylcholine receptors (M1 shown)**Trihexyphenidyl ⓘ The figure shows tiotropium, another muscarinic antagonist, in the human M1 receptor; trihexyphenidyl blocks the same acetylcholine binding site. **Target in 3D:** Muscarinic acetylcholine receptors (M1 shown). PDB structure 5CXV (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/5CXV) · Drag to rotate · pinch to zoom ## Mechanism of action Trihexyphenidyl is a parasympatholytic (antimuscarinic) drug that enters the brain. In the striatum it blocks the acetylcholine released by cholinergic interneurons, which predominates when dopamine falls, easing tremor and rigidity and the extrapyramidal effects of dopamine-blocking drugs. - Dopamine loss leaves striatal acetylcholine unopposed - Trihexyphenidyl blocks central muscarinic receptors - Tremor, rigidity and drug-induced dystonia ease ## Pharmacokinetics **Absorption** Given by mouth as tablets or oral solution **Distribution** Enters the brain ## Indications - Adjunct in all forms of parkinsonism, often with levodopa [Parkinson disease →](https://durgical.com/en/conditions/parkinson-disease/) - Extrapyramidal disorders caused by phenothiazines, thioxanthenes, butyrophenones and similar drugs [Antipsychotic-induced movement disorders (dystonia, akathisia, parkinsonism, tardive dyskinesia) →](https://durgical.com/en/conditions/antipsychotic-induced-movement-disorders/) ## Adverse effects ### Common - Dry mouth, blurred vision, dizziness - Nausea, constipation - Difficulty urinating - Nervousness; euphoria (misuse has been reported) ### Serious (rare, important) - Precipitation of angle-closure glaucoma; blindness after long-term use has been reported - Confusion, delirium and hallucinations, especially over age 60 - Anhidrosis and hyperthermia - Urinary retention and bowel obstruction ## Contraindications - Narrow-angle glaucoma - Hypersensitivity to trihexyphenidyl - Caution: prostate enlargement, gut or urinary obstruction, older adults ## Key interactions **Antipsychotics, tricyclics, antihistamines and other anticholinergics** Additive anticholinergic burden: confusion, ileus, heat intolerance **Alcohol and sedatives** More drowsiness and confusion ## What is monitored - Eye examination (gonioscopy) before starting and intraocular pressure during treatment - Cognition and behaviour, especially in older adults - Urination, bowel habit and temperature in hot weather ## Administration and safety - Tablets and oral solution: the solution is measured with an oral syringe or measuring device - Withdrawn gradually to avoid rebound parkinsonism - Can be given with food if it upsets the stomach ## Nursing care - Ask about blurred vision or eye pain (angle closure) - Check for urinary retention and constipation - Screen older adults for confusion and fall risk - Teach to avoid overheating and keep hydrated ## Pregnancy and breastfeeding It is not known whether it harms the fetus; it is used in pregnancy only if clearly needed. ## Memory aid «TriHEXyphenidyl puts a HEX on old eyes, old bladders and old brains»: glaucoma, retention, confusion. ## Test yourself Think of the answer, then tap the question to see it. ## Which test is recommended before starting trihexyphenidyl? An eye examination with gonioscopy, because it can precipitate angle-closure glaucoma. ## Why is trihexyphenidyl usually avoided in people over 65? Sensitivity to antimuscarinic effects increases with age: confusion, delirium, retention and constipation. ## Which Parkinson symptom responds best to anticholinergics? Tremor (with some effect on rigidity). [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/trihexyphenidyl/) ## Related drugs - [Benzatropine](https://durgical.com/en/pharmacology/benzatropine/) - [Biperiden](https://durgical.com/en/pharmacology/biperiden/) ## Related conditions - [Parkinson disease](https://durgical.com/en/conditions/parkinson-disease/) - [Antipsychotic-induced movement disorders (dystonia, akathisia, parkinsonism, tardive dyskinesia)](https://durgical.com/en/conditions/antipsychotic-induced-movement-disorders/) [← Back to the class: Antiparkinson anticholinergics](https://durgical.com/en/pharmacology/classes/antiparkinson-anticholinergics/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [DailyMed - TRIHEXYPHENIDYL HYDROCHLORIDE solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=e8e2ac3b-80dc-4449-9365-2586d6d57e10) (DailyMed (U.S. National Library of Medicine), 2026); [Trihexyphenidyl: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682160.html) (MedlinePlus (U.S. National Library of Medicine), 2018); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 21 (McGraw Hill, 2023). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/trihexyphenidyl/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/trihexyphenidyl/