The role of gut microbiome in the pathophysiology of PTSD, depression, and anxiety disorders.

Posttraumatic stress disorder (PTSD), depression, and anxiety disorders are prevalent and often overlapping mental health conditions with complex, multifactorial etiologies. Growing evidence implicates the gut microbiome in their pathophysiology through immune modulation, neurotransmitter regulation, and bidirectional gut-brain signaling. Findings remain fragmented and difficult to reconcile due to differences in study populations, clinical contexts, and analytic methods. This structured narrative review synthesizes current evidence on gut microbial alterations in PTSD, depression, and anxiety, while examining methodological sources of heterogeneity. We searched four databases: PubMed, Scopus, Web of Science, and PsycINFO, and identified 64 eligible studies assessing the gut microbiome composition in these disorders. Sample sizes ranged from small, exploratory cohorts (≈20 participants) to large population-based datasets (>1000 participants), with most studies conducted in China. Stool sampling and DNA extraction protocols varied widely, although 16S rRNA gene amplicon sequencing of the V3-V4 region on Illumina platforms predominated. Alpha-diversity results were inconsistent, whereas beta-diversity analyses distinguished cases from controls. Across these disorders, alterations in microbial composition was observed, including enrichment of proinflammatory and depletion of beneficial bacterial taxa. The current findings indicate that that the gut microbiome represents a promising avenue for biomarker discovery and therapeutic innovation.