Eight week open-label flexible dose trial in adult outpatients diagnosed with Major Depressive Disorder (MDD) who have had a prior failure with escitalopram. Failure is operationally defined as either premature discontinuation because of side effects or the report of an incomplete response to escitalopram, minimum dose 10mg/day, maintain for 3 weeks or more. 10mg/day was chosen because 1) it is the most commonly prescribed single dose of escitalopram in clinical practice, 2) it is equivalent to approx. 30mg/day of arcemic citalopram and 3) escitalopram has very high potency at the serotonin transporter (Ki=1.1); this means that escitalopram would be expected to saturate the transporter at relatively low doses. A total of twenty patients will be treated.
