The objective of this study is to evaluate the safety and efficacy of Hypidone Hydrochloride tablets in treatment of patients with major depressive disorder (MDD) by evaluating the change of MADRS total scores from baseline to week 6.

A total of 240 major depressive disorder (MDD) subjects between the ages of 18-65 who have current major depressive disorder diagnosed by DSM-5 will be recruited, Eligible patients will be randomized with a 1:1:1:1 ratio into the 4 treatment arms to receive either Hypidone Hydrochloride tablets or placebo, and will be accepted into the protocol after review and providing voluntary written informed consent forms and completion of a comprehensive medical and psychiatric history, physical examination, mental status examination, and routine laboratory assessment.

The subjects will accept the drug treatment twice daily orally for 6 weeks. During the treatment follow up will occur at 8±1 days after treatment, 15±1 days after treatment, 29±2 days after treatment , 43±2 days after treatment to evaluate the safety and efficacy of the drug.

Inclusion Criteria:

1. Outpatient or Inpatient, 18-65 years old, male or female
2. Current major depressive disorder diagnosed by DSM-5, single episode(296.21, 296.22, 296.23), or recurrent episode(296.31, 296.32, 296.33)
3. Montgomery-Åsberg Depression Rating Scale (MADRS) total scores in both Screening and Baseline ≥ 26
4. The first item of MADRS in both Screening and Baseline ≥ 3
5. CGI-S in both Screening and Baseline ≥ 4
6. Able to provide written informed consent forms

Exclusion Criteria:

1. Subjects accord with other mental disorders diagnosed by DSM-5
2. Subjects who attempted to suicide, or who presently have a high risk of suicide, or with the tenth item (Suicidal ideation) of C-SSRS ≥ 3
3. Baseline total scores compared with the screening period, the reduction rate of MADRS ≥ 25%
4. Subjects with serious or uncontrolled cardiovascular disease, liver disease, kidney disease, blood disease, endocrine disease, respiratory disease
5. Subjects with clinically significant ECG abnormal (Male QTcF ≥ 450 msec, Female QTcF ≥ 470 msec)
6. Treatment with a MAOI within the 2 weeks prior to the first dose of trial medication
7. Practicing 2 different treatment methods of antidepressants as recommended dose of full course (≥6 weeks)
8. Subjects who have had a Vagus Nerve Stimulation (VNS) device implanted, or who have received Modified Electric Convulsive Therapy (MECT) or Transcranial Magnetic Stimulation (TMS) within 3 months of Screening, or who received light treatment, laser treatment, acupuncture and other Chinese medicine treatment, biofeedback treatment within 2 weeks of Screening
9. Subjects with a history of true allergic response to more than 1 class of medications
10. Subjects who participated in a clinical trial within the last 30 days