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Expected pharmacological effect
Causality assessment · Expected pharmacological effect
Trihexyphenidyl and Hallucination: is the FAERS signal real?
A written Bradford Hill assessment of one drug–event pair. The grade is a judgement about the signal, not a statement that this drug causes this event in any one person; FAERS counts are reports, not rates.
Trihexyphenidyl ↔ Hallucination
n=36 co-reports · PRR 10.1 · ROR 10.5
Trihexyphenidyl is a centrally acting anticholinergic for parkinsonism; by blocking muscarinic receptors in the brain it causes confusion, hallucinations, and in overdose an anticholinergic delirium (36 co-reports, PRR 10.1). It is abused recreationally for its euphoric effects, which further increases the risk of psychosis.
Regulatory basis: trihexyphenidyl prescribing information — anticholinergic CNS effects; caution in the elderly.
| Bradford Hill viewpoint | Status | Note |
|---|---|---|
| Temporality (necessary) | met | Psychosis emerges with dosing or overdose |
| Strength | met | PRR 10.1, large |
| Consistency | met | Reproduced across anticholinergics |
| Specificity | partial | Shared across the class |
| Biological gradient | met | Dose-related |
| Plausibility | met | Central muscarinic blockade |
| Coherence | met | Fits the mechanism |
| Experiment | met | Case series support it |
| Analogy | met | Analogous to benztropine CNS effects |
This table is this page's own qualitative read of the literature cited above, not an automated or citation-gated assessment — see the note at the bottom of this page.
✗ No ClinicalTrials.gov results-posting trial in the top search hits for trihexyphenidyl-hydrochloride captured hallucination as a tracked adverse event in a usable structure. Anticholinergic trials reported CNS effects among general adverse events rather than as clean per-arm table entries.