1. Aged 18-65 years (including 18 and 65), no gender restriction, Han Chinese ethnicity.
2. Meets the diagnostic criteria for depressive disorders according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), confirmed by the Mini-International Neuropsychiatric Interview, version 5.0 (MINI).
3. Outpatients or inpatients; Hamilton Depression Rating Scale-17 items (HAMD-17) score ≥17; Hypomania Checklist-32 (HCL-32) score ≤13; and Clinical Global Impressions-Severity (CGI-S) score ≥4.
4. First depressive episode (duration ≤3 months), with no use of antidepressants or other psychotropic medications in the past 3 months.
5. Written informed consent obtained from the patient.
You may not be if
1. Meet DSM-IV diagnostic criteria other mental disorders, including schizophrenia spectrum and other psychotic disorders, bipolar and related disorders, obsessive-compulsive disorder, etc..
2. Individuals with intellectual disabilities or who are unable to cooperate for other reasons, or those lacking or having incomplete civil capacity during the onset of illness;
3. Suffering from neurological or organic brain diseases (such as stroke, cerebral hemorrhage, brain tumors, Parkinson's disease, epilepsy, etc.) and a history of severe traumatic brain injury;
4. Have attempted suicide within the past 3 months, or currently present a high suicide risk, defined as a Montgomery-Åsberg Depression Rating Scale (MADRS) item 10 score ≥5.
5. Are pregnant or breastfeeding, cannot use reliable contraception during the study, or plan to conceive (or impregnate a partner) within 3 months after study initiation.
6. Have known allergies to escitalopram oxalate or its excipients.
7. Are currently taking medications that may interfere with the evaluation of escitalopram efficacy.
8. Have participated in another drug clinical trial within the past 3 months.
9. Have contraindications to MRI scanning, such as metal implants or claustrophobia.
10. Considered unsuitable for study participation by the investigators for any other reason.
