A case-report of paranoid psychosis that developed in association with fluoxetine treatment is presented. Psychotic symptoms completely resolved after two weeks of treatment with risperidone. The patient has never before experienced psychotic symptoms and her psychopathology during the fluoxetine treatment did not correspond to her previous psychiatric complaints. In the last decade, there were published several case histories describing psychotic paranoid symptoms associated with fluoxetine treatment. However, the pathogenesis of psychosis induced by a SSRI preparation is not quite clear. New antipsychotics that bind with 5HT receptors support the arguments for a role of serotoninergic neurotransmission in psychosis. Fluoxetine increases the synaptic availability of serotonin. The possible explanation for psychosis may be down-regulation of serotonin inhibitory receptors on dopaminergic neurons of mesolimbic neuronal pathway or lowering of the serotoninergic tonus in consequence of presynaptic 5HT3 autoreceptor stimulation. Our case history is intended as a reminder, that psychosis can develop as a rare undesirable effect during treatment with fluoxetine and perhaps other SSRI in some patients.

        Key words: fluoxetine, paranoid psychosis, serotonin, side effects.