The purpose of this study is to determine the efficacy of SA4503 compared to placebo in the treatment of subjects with major depressive disorder (MDD). Secondary, to evaluate the safety of SA4503 compared to placebo in subjects with MDD.

Further study details as provided by M's Science Corporation:

Inclusion Criteria:

• Male or female between the ages of 18 and 65 (inclusive)
• Diagnosis of MDD according to the Diagnostic and Statistical Manual of Mental Disorders (DSM)-IV criteria and a shortened MINI evaluation
• HAM-D17 score of >/= 21 and a severity score of at least 2 for Item 1 (depressed mood) at both Screening and Baseline
• Current depressive episode of at least 3 months duration, and significant depressed mood and anhedonia in the 4 weeks prior to Screening.

Exclusion Criteria:

• Subjects who have received fluoxetine within 1 month prior to Baseline or any other antidepressant within 2 weeks prior to Baseline, or any unlicensed medication within 1 month before Screening
• Subjects who require psychotropic medication other than the study medication
• Subjects who started psychotherapy within 4 months prior to Screening
• Subjects who currently (i.e., in the month prior to Screening) meet DSM-IV criteria for bipolar syndrome or psychotic depression or severe somatoform or eating disorders
• Subjects who have a primary diagnosis of anxiety
• Subjects who regularly use sleeping medication more than 3 times per week
• Subjects who have major psychiatric or neurologic disorders other than MDD
• Subjects with depression secondary to stroke, cancer, or other severe medical illness
• Subjects who have a history of alcohol or substance dependence(within 1 year prior to Screening)