Clinical Research Directory

Inclusion criteria 1. Aged 12-18 years; 2. Meets DSM-5 criteria for major depressive disorder (MDD) and is currently in a depressive episode according to the Kiddie Schedule for Affective Disorders and Schizophrenia - Present and Lifetime Version (K-SADS-PL) interviews; 3. Child Depression Rating Scale-Revised (CDRS-R) score ≥40 at baseline; 4. Clinical Global Impression Scale (CGI-S) score ≥ 4 at baseline. Exclusion criteria 1\. Presence of any comorbid psychiatric disorder according to DSM-5, other than anxiety disorders; 2. MDD with psychotic symptoms; 3. Young Mania Rating Scale (YMRS) \>13 at baseline; 4. History of neurological disorders (e.g., epilepsy, traumatic brain injury), or the presence of serious physical illnesses (e.g., thyroid disease, lupus erythematosus, diabetes mellitus, clinically significant pulmonary, hepatic, or renal impairment, or major trauma); 5. Nonresponse to at least two antidepressants with different mechanisms, and each administered at an adequate dose and for an adequate duration; 6. History of intolerance to sertraline or nonresponse to an adequate therapeutic course of sertraline; 7. Current high suicide risk; 8. History of alcohol or drug abuse or dependence; 9. Taking or administering antidepressants within 5 half-lives; 10. Use of probiotic-related food or medicine within 2 weeks before enrollment; 11. Systemic use of antibiotics or antifungals within 1 month before enrollment; 12. History of severe food allergy or known hypersensitivity to the Lactobacillus crispatus preparation or any of its components; 13. Adherence to vegetarian or other restrictive dietary patterns; 14. Pregnancy or breastfeeding.