Efficacy and Safety of S 47445 Versus Placebo as Adjunctive Treatment in Depressed Patients Not Fully Recovered From Depressive Symptoms With a Current Antidepressant Treatment

Inclusion Criteria: * Outpatients * Fulfilling DSM-5 criteria for Major Depressive Disorder confirmed by the brief structured interview M.I.N.I. (single or recurrent episode, current episode ≤ 12 months, current depressive episode of moderate or severe intensity, with or without anxious distress, with or without melancholic features, without mixed features or atypical features, without seasonal pattern, without psychotic features, without catatonic features, without peripartum onset for the current episode) * Patients treated for the current depressive episode with an antidepressant treatment with SSRI (fluoxetine, citalopram, paroxetine, escitalopram or sertraline) given in monotherapy at recommended dose for at least 6 weeks and no more than 4 months and with a stable dosage for at least 3 weeks * HAM-D total score ≥ 20 * Clinical Global Impression Severity of illness (item 1): 6 ≥ CGI-S ≥ 4 * Antidepressant Treatment Response Questionnaire (ATQR) \< 50% for the current SSRI * Absence of any abnormalities likely to interfere with the conduct of the study (ECG, vital signs, laboratory tests, medical history) Exclusion Criteria: * Depressive episode of mild intensity according to DSM-5 criteria * All types of depressive episodes other than those occurring in a Major Depressive Disorder (Persistent Depressive Disorder (Dysthymia) according to DSM-5 criteria, including persistent depressive disorder with intermittent or persistent major depressive episode according to DSM-5, Premenstrual Dysphoric Disorder, Substance Induced Depressive Disorder, Depressive Disorder due to another Medical Condition, Other Specified or Unspecified Depressive Disorder, Bipolar Disorder I or II, depressed episode, Schizoaffective Disorder (Depressive or Bipolar type)) * Depression onset within 12 months after a stroke * Suicidal risk defined as a score \> 3 on the item 3 of the HAM-D scale or in the investigator's opinion * Lactose intolerance * Patients with hereditary problems of galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption * Resistant depression for the current episode (patients who have not responded to 1 previous antidepressant treatment before the SSRI taken at an appropriate dose) * Current panic disorder * Obsessive compulsive disorder * Current post traumatic stress disorder, current acute stress disorder * Current or past psychotic disorder * Any severe personality features