Inclusion Criteria:
1. The subject voluntarily signs the informed consent form and is able to comply with the scheduled visits, treatment plan, laboratory tests and other study procedures;
2. Aged 18 years and above, male or female;
3. Outpatients with the main diagnosis of depression meeting DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, 5th Edition) diagnostic criteria for recurrent episodes (without psychotic features) (F33.1/F33.2);
4. MADRS total score ≥ 26 at baseline of screening and open treatment phase.
Exclusion Criteria:
1. Patients who meet the criteria of treatment-resistant depression, that is, patients who have failed to respond to at least two antidepressants with different mechanisms of action in the case of adequate treatment (at least 8 weeks of treatment at the maximum recommended therapeutic dose);
2. Known to have a history of allergy to any component of the investigational product or similar drugs, or allergic constitution (allergic to two or more drugs or food) and the investigator considers it inappropriate to participate in the trial;
3. Significant suicide attempt (defined as a score of ≥ 4 on item 10 of the MADRS scale) or suicidal behavior in the past 6 months on the Columbia-Suicide Severity Rating Scale (C-SSRS) ("actual attempt","interrupted attempt", and"abandoned attempt"with any outcome of"yes");
4. Other diseases meeting DSM-5 diagnostic criteria, including organic mental disorders, substance-related and addictive disorders (except nicotine or caffeine), schizophrenia spectrum and other psychotic disorders, bipolar and related disorders, substance/drug-induced depressive disorders, depressive disorders due to other physical/mental diseases, obsessive-compulsive and related disorders, traumatic and stress-related disorders, dissociative disorders, anorexia nervosa or bulimia, personality disorders;
5. Previous history of increased intraocular pressure or closed glaucoma;
6. Patients with poorly controlled hypertension \[screening or baseline sitting systolic blood pressure (SBP) ≥ 160 mmHg or sitting diastolic blood pressure (DBP) ≥ 100 mmHg\];
7. Total bilirubin (TBIL) value 1.5 times higher than the upper limit of normal, or alanine aminotransferase (ALT) or aspartate aminotransferase (AST) 3 times higher than the upper limit of normal, or creatinine 1.5 times higher than the upper limit of normal at screening;
8. Female patients who are pregnant or have a positive pregnancy test result, or male and female subjects of childbearing potential do not agree to use effective contraception throughout the study and for at least 1 month after discontinuation;
9. Patients who received electroconvulsive therapy (ECT) within 3 months before screening or currently require ECT according to the investigator's judgment;
10. Patients who have received or are receiving systemic psychotherapy (interpersonal therapy, dynamic therapy, cognitive behavioral therapy) within 3 months before screening or currently need systemic psychotherapy according to the investigator's judgment;
11. Patients who received physical therapy such as transcranial magnetic stimulation (TMS), deep brain stimulation, vagus nerve stimulation and transcranial electrical stimulation within 3 months before screening;
12. Patients who received phototherapy within 2 weeks before screening;
13. Patients who have stopped antidepressant drugs for less than 5 half-lives (at least 2 weeks for monoamine oxidase inhibitors (MAOIs) and 1 month for fluoxetine) before enrollment;
14. Those who have participated in other clinical trials within 1 month before screening (excluding those who are not eligible after screening and not enrolled);
15. Currently suffering from acute or severe unstable physical illness, or other conditions that the investigator judges the subject is not suitable for the study.
