Efficacy and Safety of Sertraline Combined With Lactobacillus Crispatus in Adolescents With Depression

The goal of this clinical trial is to evaluate the efficacy and safety of sertraline combined with Lactobacillus crispatus in adolescents aged 12-18 years with major depressive disorder. The main question it aims to answer is: Whether sertraline combined with Lactobacillus crispatus is superior to sertraline combined with placebo in reducing depressive symptoms and improving emotional symptoms in adolescents with depression. If there is a comparison group: Researchers will compare sertraline combined with Lactobacillus crispatus with sertraline combined with placebo ( look-alike substance that contains no probiotics) to determine whether the addition of Lactobacillus crispatus provides greater therapeutic benefit in adolescents with depression. Participants will: 1. Receive sertraline combined with Lactobacillus crispatus or sertraline combined with placebo for 8 weeks; 2. Attend clinic visits every 4 weeks for clinical assessments and safety monitoring