Genistein is a polyphenolic molecule and the active form of the soy isoflavone, genistin. It has both phytoestrogen and protein tyrosine kinase inhibiting properties. Since tyrosine phosphorylation is involved in central nervous system regulation of neurotransmission inhibition by genistein may be a novel strategy to directly modulate synaptic activity and treat neuropsychiatric illnesses. Genistein's specific hormonal properties may also have salutary effects on brain function in depressed patients. Genistein increases dopamine and other monoamine activity, affects neurotrophic factor transcription, and has neuroprotective properties.