Inclusion Criteria:

• Male and female outpatients between the ages of 18 and 70.
• Patients with a principal DSM-IV diagnosis of Major Depressive Disorder, unipolar, nonpsychotic type
• Patients with a total of 14 or higher on the 17-item Hamilton Depression Scale at baseline

• Patients who have had treatment with an SSRI at an adequate dose (see Table for a minimum of 6 weeks (i.e.

  6 wks at the dose defined as adequate in Table 2)

• Patients who agree to use acceptable method of birth control throughout the study

Exclusion Criteria:

• Patients with any of the following DSM-IV diagnoses: Delirium, Dementia, Amnestic, or other Cognitive Disorders. Bipolar Disorder or cyclothymia, Schizophrenia, Delusional (Paranoid) Disorders and Psychotic Disorders not elsewhere classified, Severe Borderline Personality Disorder, Anorexia Nervosa, or Bulimia.
• Patients who, within the past 6 months, met DSM-IV criteria for abuse of or dependence on any drug, including alcohol.
• Patients who are pregnant or nursing women.
• Patients who would pose a serious risk for suicide during the course of the study, as evidenced by one of the following: (a) report of having a specific plan for killing themselves, (b) a score of 3 or higher on the Hamilton Depression Rating Scale item #3 as rated by the treating clinician at Week 0, or (c) a suicide attempt within the last 6 months which required medical attention, such as an emergency room visit or which is considered by the treating physician to have been possibly life threatening
• Patients with unstable medical conditions such as untreated or uncontrolled hyperthyroidism, hypothyroidism, hypertension (defined as blood pressure>150/90), cardiovascular disease, diabetes, HIV (by report of patient).
• Patients with a history of seizures.