Platelet monoamine oxidase activity in acute schizophrenia: relationship to symptomatology and neuroleptic medication.

Platelet MAO activity was assessed in 35 schizophrenics during a trial of the isomers of flupenthixol. Enzyme activity was unrelated to severity of symptoms, the presence of delusions, hallucinations or thought disorder or to negative symptoms. In a few patients MAO activity fluctuated widely with time, but in the group of patients on medication there was a slow decrease in enzyme activity which was significant after 28 days of treatment. Enzyme activity after 14 days' drug treatment was still correlated with activity before treatment, but after 28 days this significant correlation disappeared. Slow effects of neuroleptic drugs on platelet MAO activity may explain previous findings of reduced activity of the enzyme in schizophrenia.