Section 03 · Monograph

Trihexyphenidyl

Reviewed Nov 2026FDA label

ArtaneAnticholinergic

Indications

Adjunctive treatment in all forms of parkinsonism (idiopathic, postencephalitic, and arteriosclerotic types), often used with levodopaFDA-labeled
Control of extrapyramidal disorders (drug-induced parkinsonism) caused by antipsychotic agents such as phenothiazines and butyrophenonesFDA-labeled

Synthetic anticholinergic (antimuscarinic) agent that exerts a direct inhibitory effect on the parasympathetic (cholinergic) nervous system, similar in profile to atropine but with a milder side-effect burden
Reduces the relative cholinergic excess that occurs in the striatum when dopaminergic tone is reduced (Parkinson's disease) or blocked (antipsychotic-induced parkinsonism)
Also has direct musculotropic (smooth-muscle relaxant) activity

Idiopathic Parkinson's disease: initiate 1 mg on day 1, then increase by 2 mg increments every 3–5 days until total daily dose of 6–10 mg is reached; some patients (notably postencephalitic parkinsonism) may need 12–15 mg/day
Drug-induced (postencephalitic/arteriosclerotic) parkinsonism: total daily dose typically 5–15 mg, individualized
When added to levodopa: usual trihexyphenidyl dose is 3–6 mg daily in divided doses; dose reduction of one or both agents may be needed
Doses greater than 10 mg/day should be divided into 4 portions rather than 3
Administer in divided doses at mealtimes (or after meals if excessive dry mouth occurs); may give at bedtime if drooling/nighttime symptoms predominate
Elderly patients (>60 years): initiate at low dose with slow, careful upward titration due to increased sensitivity to anticholinergic effects

Known hypersensitivity to trihexyphenidyl
Angle-closure glaucoma — parasympatholytic activity of trihexyphenidyl may precipitate or worsen angle-closure glaucoma; label directs gonioscopic evaluation and regular intraocular pressure monitoring
Use with caution/avoid in obstructive disease of the gastrointestinal or genitourinary tract
Use with caution in elderly males with possible prostatic hypertrophy

Additive anticholinergic burden with other anticholinergic drugs (antihistamines, tricyclic antidepressants, other antiparkinsonian anticholinergics)
May require dose reduction of concomitant levodopa or of trihexyphenidyl itself when combined
Can be used to reduce required dosage of antipsychotic-class tranquilizers when treating drug-induced extrapyramidal symptoms
Additive CNS depressant/sedative effects with alcohol and other CNS depressants
Caution with other drugs impairing GI motility (risk of paralytic ileus) or urinary retention

Dry mouth, blurred vision, dizziness — reported in roughly 30–50% of patients; often diminish with continued use or dose adjustment
Mild nausea, nervousness
Constipation, drowsiness
Urinary hesitancy or retention
Tachycardia, pupil dilation, increased intraocular pressure
Mental confusion, agitation, disturbed behavior — especially in patients with arteriosclerosis or idiosyncratic drug sensitivity
Psychiatric manifestations: delusions, hallucinations, paranoia (rare but serious)
Rare: suppurative parotitis, paralytic ileus/colonic dilation, angle-closure glaucoma
Tardive dyskinesia may become unmasked or aggravated during long-term anticholinergic therapy

Baseline gonioscopic evaluation and regular intraocular pressure monitoring, particularly in patients at risk for angle-closure glaucoma
Cognitive/mental status monitoring, especially in elderly patients — watch for confusion, hallucinations, agitation
Monitor for urinary retention and constipation/bowel function, especially in men with prostatic hypertrophy
Reassess ongoing need periodically; use lowest effective dose given cumulative anticholinergic risk
Monitor heart rate for tachycardia
Careful, slow dose titration and closer monitoring in patients over 60 years of age

Manufacturer labeling does not provide a specific pregnancy risk category or detailed pregnancy safety data
No specific labeling guidance on use during lactation; anticholinergic agents are generally used cautiously in breastfeeding given potential to reduce milk production and cause infant anticholinergic effects
Use in pregnancy/lactation only after individualized risk-benefit assessment