Adjunctive fecal microbiota transplantation for major depressive disorder: A randomized, double-blind, placebo-controlled trial.

Gut microbiota may influence antidepressant treatment outcomes, yet whether targeted modulation can enhance efficacy remains unclear. We conducted a randomized, double-blind, placebo-controlled trial in patients with major depressive disorder, administering a 2-week course of fecal microbiota transplantation (FMT) capsules or placebo as an adjunct to escitalopram (ChiCTR2300071421). Remission rates at week 8 did not differ significantly between groups, but FMT produced greater reductions in Hamilton Depression Rating Scale, 17-item version (HAMD-17) scores at weeks 2 and 8. FMT was well-tolerated with a safety profile comparable to placebo. Multi-omics analyses show durable donor microbial engraftment and enrichment of beneficial Lachnospiraceae and Oscillospiraceae taxa. Microbial remodeling is accompanied by an increase in serum bile acids that correlate with the alleviation of depressive symptoms. Mediation analysis supports a bile-acid-mediated suppression of inflammatory pathways linking microbial changes to antidepressant effects. Overall, FMT may provide a safe avenue to enhance escitalopram efficacy through microbiota-directed regulation of bile-acid metabolism and inflammation.