Hello! If you are depressed or have a depressive state for the first time, we invite you to learn about the following information [Project Information] This study is a scientific project conducted with key funding from the National Key Basic Research and Development Program (973 Program), which aims to establish objective diagnostic indicators and individualized intervention methods for major depressive disorder. The Sixth Hospital of Peking University is the lead unit of this project. By comparing patients and healthy people, collecting treatment-related information, and through comprehensive analysis, doctors will screen indicators that can guide antidepressant treatment, and finally establish a guidance system for evaluating the efficacy of depression treatment and individualizing treatment. Benefits】If you meet the study inclusion criteria for diagnostic indicators and individual interventions, you will be assigned to the appropriate study/control group to receive assessment and treatment of your psychological and physical conditions. You will be provided with a full set of free psychological assessments during the study, and appointments and follow-up visits will ensure that you receive standardized, individualized treatment. We will answer your medical questions face-to-face and follow up on your recovery process. Clinical assessment: Before (and/or at the end of) 2, 4, 8 weeks (and/or at the end of) 6 months, 1 year and 2 years of your treatment, your doctor will take a medical history, assess clinical scales and relevant questionnaires to get a full picture of your clinical characteristics, disease severity, cognitive and emotional improvement, and adverse reactions. Laboratory measurements: Before your medication (and/or after the acute treatment), the doctor will perform a physical examination and relevant laboratory tests (including: taking 5ml of venous blood, EEG, polysomnography, evoked event potentials) respectively. The principles of participation and privacy protection] You are completely free to participate or not in the study or to withdraw in the middle of the study, and your subsequent medical treatment will not be affected by this. Your clinical data and other information are entered into the database in the form of a code, which does not contain any personally identifiable information. We will keep your identity and privacy strictly confidential at all times.