This trial includes a short-term study and a long-term study. The short-term study is a multicenter, randomized, double-blind, placebo-controlled parallel-group study with a 6-week duration. The long-term study is a multicenter, open-label, single-arm study with a maximum duration of 27 weeks.
Age: 18 to 65 years old (inclusive), Male or female.
Based on investigator's clinical assessment, study participants meet the diagnostic criteria for Major Depressive Disorder (MDD) as defined in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), with a diagnosis of single episode or recurrent episodes (ICD-10 codes: 296.2/296.3), without psychotic features. For patients with first-episode depression, the current episode must have a duration of ≥3 months; for patients with recurrent depression, the current depressive episode must have a duration of ≥1 month
Depressive episode confirmed by the Mini International Neuropsychiatric Interview Version 7.0.0 (M.I.N.I. 7.0.0).
Patients must have a 17-item Hamilton Depression Rating Scale (HAM-D17) total score ≥24, a Clinical Global Impression-Severity (CGI-S) score ≥4, and a score ≥2 on Item 1 (Depressed Mood) of the HAM-D17 at screening and baseline
Other psychiatric disorders meeting DSM-5 criteria, including but not limited to schizophrenia spectrum and other psychotic disorders, bipolar and related disorders, panic disorder, agoraphobia, social anxiety disorder, obsessive-compulsive disorder, post-traumatic stress disorder, generalized anxiety disorder, anorexia nervosa and bulimia nervosa, neurodevelopmental disorders, schizoaffective disorder, or any other psychiatric disorder that, in the Investigator's judgment, may compromise subject compliance.
A reduction of ≥25% in HAM-D17 total score at baseline compared with the screening visit (this criterion does not apply if baseline and screening assessments are performed at the same visit).
A score ≥4 on Item 10 (Suicidal Thoughts) of the MADRS;
An answer of "Yes" to Question 4 (active suicidal ideation with intent without specific plan) or Question 5 (active suicidal ideation with specific plan and intent) of the C-SSRS within the past 6 months at screening, or a suicide-related behavior within the past 6 months (any "Yes" response for Actual Attempt, Interrupted Attempt, or Aborted Attempt).