PURPOSE OF REVIEW: Gut microbiota and its alterations have been increasingly implicated in the pathophysiology of major psychiatric disorders via the microbiota-gut-brain axis. This narrative review aims to highlight current findings from recent systematic reviews and meta-analyses (published between September 2023 and March 2025), addressing the role of gut microbiota in major depressive disorder (MDD) and schizophrenia, with particular attention to the effects of psychotropic medications and microbiota-targeted interventions.
RECENT FINDINGS: In MDD, consistent changes in gut microbiota composition, such as depletion of Faecalibacterium and enrichment of Bifidobacterium, have been reported, although alpha diversity findings remain inconsistent. Antidepressants may modulate microbiota in both humans and animal models, while probiotic and synbiotic interventions yield modest reductions in depressive symptoms and inflammatory markers. In schizophrenia, observational studies showed stable alpha diversity, but altered beta diversity, with taxa like Bifidobacterium , Lactobacillus , and Roseburia linked to symptom severity, cognition, and antipsychotic exposure. Interventional studies, though limited, suggest small-to-moderate clinical improvements with probiotic supplementation, and emerging evidence supports potential benefits for both cognition and reducing metabolic side effects of psychotropic medications.
SUMMARY: Across depressive and psychotic disorders, growing evidence supports a multifaceted and indispensable role of gut microbiota in clinical symptomatology, treatment response, and cognition of patients. However, substantial variability of methodological frame, limited sample sizes, lack of mechanistic precision, and heterogeneity between published studies result in unequivocal conclusions on the exact effect of microbiota on mental health in general, and on major psychiatric disorders. While microbiota-targeted therapies remain adjunctive and exploratory, recent findings reinforce them as a promising target for more successful treatment of mental health disorders in the near future. In order to reach that goal, we need more rigorous, longitudinal, and integrative studies to guide the clinical implementation.
