This is an 8-week double blind parallel study that will examine the efficacy and safety of Novasoy® (Registered Trademark) (CAS 446-72-0), a marketed botanical dietary supplement, in acutely depressed male and female patients (n&eq;60 in each group). The study has two Periods. Study Period I is a washout phase (1 week) and evaluation period. Study Period II is a monotherapy 8-week parallel, placebo controlled, acute treatment phase in which the efficacy and tolerability of isoflavones is compared to baseline. After completing the 8-week study period, subjects will be followed at the mood disorders clinic at NIMH for any necessary treatment adjustment and referred back to their clinician for further treatment.