Effect of probiotic supplement on improvement of depressive symptoms in patients with substance-induced depressive disorder: a randomized, double-blind, placebo-controlled clinical trial

In this randomized, double‑blind, placebo‑controlled pilot trial, both probiotic and placebo groups showed significant improvements in depressive and anxiety symptoms over time, with no significant between‑group differences. Probiotic supplementation was associated with non‑significant trends in selected inflammatory markers, suggesting possible immunological effects that warrant further investigation. Larger, multicenter trials with comprehensive microbiome and immunologic assessments are needed to clarify the potential role of probiotics as an adjunctive strategy in substance‑induced depressive disorder.