Mianserin treatment of patients with psychosis induced by antiparkinsonian drugs.

We evaluated the effects of mianserin, a relatively selective 5-HT2 receptor antagonist, on symptoms related to drug-induced psychosis in patients with Parkinson's disease (PD). A total of 12 patients with PD who had developed drug-induced psychosis showed delirium (DSM-III-R criteria; n = 10) and pure visual hallucinations (n = 2). The antiparkinsonian drugs involved in the drug-induced psychosis were L-DOPA/carbidopa, bromocriptine, trihexyphenidyl, and amantadine. They received mianserin (mean 36.7 mg, range 20-60 mg) given orally for 8 weeks. Complete relief or marked improvement in psychotic symptoms was noted in 8 patients, moderate improvement in 2 patients, and no effect in 2 patients. The parkinsonian disability also decreased slightly in 8 patients. These results suggest that serotonin antagonism at 5-HT2 receptors may not only play an important role in the treatment of drug-induced psychosis in PD, but may also ameliorate the symptoms of parkinsonism.