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Pharmacology · Drugs and Prescriptions

Trihexyphenidyl

Cyclodolum

Trihexyphenidyl is a classic antiparkinsonian agent belonging to the group of central muscarinic acetylcholine receptor antagonists. The drug inhibits excessive cholinergic activity in the basal ganglia, effectively eliminating tremor and muscle rigidity.

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Pharmacological groupCentral muscarinic antagonists (antiparkinsonian agents)
Mechanism of actionBlockade of $M_1$ muscarinic receptors in the neostriatum
Dosage formTablets 0.001, 0.002, and 0.005 g
Specific riskAnticholinergic delirium in overdose
How to write a prescription
Rp.: Tab. Cyclodoli 0,002
D.t.d. N 50
S. Внутрь по 1 таблетке 2-3 раза в сутки во время еды

Alternative prescription formats: Tab. Cyclodoli 0.001; Tabulettas Cyclodoli 0.002; Tab. Trihexyphenidyli 0.002

Dosage form
Tablets 0.001, 0.002, and 0.005 g
Administration
Orally 0.001–0.002 g with meals (Maximum Single Dose: 0.01 g; Maximum Daily Dose: 0.02 g)
Group
Agents affecting the central nervous system
3 min readFor medical studentsUpdated 09/24/2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesReviewed by medical editor: Aulov A. A., general practitioner · 09/24/2026

Mechanism of action

Trihexyphenidyl belongs to agents that inhibit cholinergic transmission in the central nervous system. Its primary target is the $M_1$ muscarinic receptors of the neostriatum. By blocking them, the drug restores the disturbed balance between the dopaminergic and cholinergic systems characteristic of parkinsonism. An important pharmacological advantage over classical atropine is that trihexyphenidyl acts predominantly within the CNS, making its peripheral effects significantly less pronounced.

Pharmacological effects

The drug exhibits moderate antiparkinsonian activity. Clinically, it primarily and selectively suppresses tremor (shaking) and reduces muscle rigidity (stiffness). However, it is important to remember a clinical nuance: trihexyphenidyl has little effect on bradykinesia (slowness of movement).

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Indications for use

Like its derivative biperiden, trihexyphenidyl is prescribed for the following extrapyramidal disorders:

  • Parkinson's disease (primarily in the early stages of the disease).
  • Parkinsonism syndrome of various etiologies.
  • Drug-induced parkinsonism is a specific indication for this group. The drug is used to prevent and relieve extrapyramidal symptoms caused by antipsychotics (neuroleptics).

Side effects and overdose

Adverse reactions are classified according to their mechanism of occurrence (localization of the blocked receptors):

  • Peripheral (resulting from peripheral muscarinic receptor blockade): dry mouth (xerostomia), constipation, tachycardia (palpitations), urinary retention, and cycloplegia (impaired near vision).
  • Central (resulting from central muscarinic receptor blockade): cognitive impairment, including memory loss and decreased concentration. Elderly patients are at particularly high risk as they are most sensitive to central side effects.

In case of overdose, acute psychosis develops: psychomotor agitation and hallucinations (so-called anticholinergic delirium).

Contraindications

Given its pronounced anticholinergic profile, the drug is strictly contraindicated in:

  • Glaucoma (due to the risk of increased intraocular pressure).
  • Prostatic hyperplasia (high risk of acute urinary retention).
  • Lactation period (breastfeeding).
  • Individual hypersensitivity.

Prescription rules and dosages

The drug is available in tablets of 0.001 g (1 mg), 0.002 g (2 mg), and 0.005 g (5 mg). Administered orally with meals. The standard single dose is 0.001–0.002 g.

  • Maximum Single Dose (MSD): 0.01 g.
  • Maximum Daily Dose (MDD): 0.02 g.

Prescription example: Rp.: Tab. Cyclodoli 0.002 D.t.d. N. 50 S. Take one tablet orally with meals.

Briefly: answers to topical questions

How does trihexyphenidyl affect gastrointestinal tone and motility?

In the cited sources, the effect of trihexyphenidyl on gastrointestinal tone and motility is not directly described. Constipation and dry mouth are listed as peripheral side effects of biperiden, which is pharmacologically related to trihexyphenidyl.

How to memorize

Cyclodol focuses in the CNS: blocks the Center (neostriatum), inhibits Tremor, but scrambles Memory.

Class and exam questions

Why is trihexyphenidyl preferred over atropine in parkinsonism?

Trihexyphenidyl is a central muscarinic antagonist. Unlike atropine, it acts predominantly in the CNS, causing significantly fewer peripheral side effects (such as dry mouth or tachycardia).

How does the drug affect the main symptoms of Parkinson's disease?

It effectively reduces tremor and muscle rigidity, yet has virtually no effect on bradykinesia.

What is a specific indication for central anticholinergic agents?

Relief and prevention of drug-induced parkinsonism (extrapyramidal symptoms) that occurs as a side effect of neuroleptic therapy.

Why is the drug prescribed with caution in the elderly?

Elderly patients are most sensitive to central side effects of anticholinergic drugs, primarily cognitive impairment (memory loss and decreased concentration).

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What else to study on this topic

  • Comparative profile of trihexyphenidyl and biperiden
  • Mechanism of drug-induced parkinsonism during neuroleptic therapy
  • Dopamine receptor agonists (bromocriptine) in the treatment of parkinsonism
  • Principles of combination therapy with levodopa and peripheral decarboxylase inhibitors
  • Anticholinergic syndrome: clinical presentation and emergency management in overdose

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