The primary object of this study is to confirm the superiority of tianeptine compared to escitalopram on effects that improves subjective and objective cognitive impairments in patients suffering from major depressive disorder.

Along with depressive symptoms, subjective and objective cognitive impairments are frequently complained by the patients with major depressive disorder. Tianeptine acts on glutamate system and is known as a promising drug for improving cognitive impairment.

The present study aims to confirm the superiority of tianeptine compared to escitalopram on effects that improves subjective and objective cognitive impairments after a 12-week treatment in patients suffering from major depressive disorder.

Inclusion Criteria:

1. Patients fulfilling DSM-IV-TR(American Psychiatric Association, 4thedition, 2000) criteria for Major Depressive Disorder diagnosis
2. The male or female patients aged more than 40 years
3. Patients able to hand in written informed consent before his/her participation in this clinical study
4. Women of childbearing potential with negative pregnancy test during screening phase and entire study period (during entire study period, able to clearly agree with effective contraception such as contraceptive pill, progesterone injection, levonorgestrel implant, estrogen ring, transdermal contraceptive agent, intra-uterine contraceptive device, sterilization operation of husband, and double contraceptive method (e.g. combination of condom, pessary, spermicide, etc. ))
5. Patients who have subjective cognitive impairment, or who have objective cognitive impairment (MMSE ≤26) without subjective cognitive impairment
6. HAM-D(17-items) total score ≥ 16

Exclusion Criteria:

1. Patients meeting more than one following patient characteristics

   1. Patients fulfilling DSM-IV-TR current or past diagnosis of any psychiatric disorders other than major depressive disorder (i.e. manic or hypomanic episode, schizophrenia, delirium, dementia, eating disorder, obsessive-compulsive disorder, panic disorder, post-traumatic stress disorder, major depressive disorder with psychotic features, mental retardation, organic brain disorder, or psychiatric disorders due to general medical condition, according to DSM-IV-TR)
   2. Patients with any substance-related disorder (excluding nicotine) within the past 12 months, as defined in DSM-IV-TR
   3. Patients with a history or presence of any neurological disorders (e.g. multiple sclerosis, seizure, etc.)
   4. Patients with any axis II disorder that prone to interfere with the evaluation of the study

2. Patients with a history or presence of any hypersensitivity to tianeptine, escitalopram or other drugs

3. Patients who receive formal psychotherapy (e.g. cognitive behavioral therapy, insight-oriented psychoanalysis, interpersonal therapy, etc.) and who have a plan for getting psychotherapy

4. Patients with any clinically significant abnormality (e.g. hepatic failure, renal failure, cardiovascular disorder, respiratory disorder, gastrointestinal disorder, endocrine disorder, neurological disorder, inflammatory disorder, neoplasm, metabolic disorder, etc.)

5. Patients who have abnormal ECG and a significant disease according to the investigator's judgment

6. Patients with any chronic liver or kidney disease

7. Patients with a family history of long QT syndrome

8. Patients previously not responders to tianeptine or escitalopram in the treatment of major depressive disorder

9. Patients who have a suicide risk according to the investigator's judgment