Primary Objective:

• To evaluate the efficacy of three fixed doses of SSR125543 (20 mg daily, 50 mg daily, and 100 mg daily) compared to placebo in outpatients with major depressive disorder, as assessed by the change from baseline (Day -1) to Day 56 in the 17-item Hamilton Depression Rating Scale (HAM-D) total score.

Secondary Objectives:

• To evaluate the tolerability and safety of SSR125543 in outpatients with major depressive disorder
• To evaluate plasma concentrations of SSR125543

This duration of this trial is 11 weeks.

Inclusion criteria:

• Patients with a diagnosis of major depressive disorder, as defined by the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, Text Revision (DSM-IV-TR) criteria (296.3) and confirmed by the semi-structured Mini International Neuropsychiatric Interview (MINI).

Exclusion criteria:

• Inpatient hospitalization at screening
• Symptoms of depression present for <30 days or >2 years
• Significant suicide risk
• Mild depression as measured by standard clinical research scales
• History of failure to respond to antidepressant treatment
• Other psychiatric conditions that could obscure the results of the study
• For women of child-bearing potential, the unwillingness to use highly effective means of birth control

The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.