Clozapine and Trihexyphenidyl interaction
Clozapine and Trihexyphenidyl: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Clozapine (Clozaril) label · effective 2025-06-06
When possible, avoid concomitant use, with other anticholinergic medications because the risk for anticholinergic toxicity or severe gastrointestinal adverse reactions is increased [see Warnings and Precautions ( 5.7 ), Drug Interactions ( 7.1 )].
• Anticholinergic Toxicity : When possible, avoid use with other anticholinergic drugs and use with caution in patients with a current diagnosis or prior history of constipation, urinary retention, clinically significant prostatic hypertrophy, or other conditions in which anticholinergic effects can lead to significant adverse reactions.
Use with caution in patients with a current diagnosis or prior history of constipation, urinary retention, clinically significant prostatic hypertrophy, or other conditions in which anticholinergic effects can lead to significant adverse reactions.
From the Trihexyphenidyl (Trihexyphenidyl Hydrochloride) label · effective 2025-07-02
Neuroleptic Malignant Syndrome A potentially fatal symptom complex sometimes referred to as Neuroleptic Malignant Syndrome (NMS) has been reported in association with dose reduction or Discontinuation of trihexyphenidyl.
Prophylactic administration of anticholinergic agents, such as trihexyphenidyl, as a prevention of drug-induced parkinsonism during neuroleptic therapy is not recommended.
Concurrent use of alcohol or other CNS depressants with trihexyphenidyl HCl may cause increased sedative effects.
There may be an increased risk for the development of tardive dyskinesia during concomitant administration of anticholinergics and neuroleptics ( see PRECAUTIONS , General ).
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Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.