Volume 30, Issue 172, June 2026

The gut–brain axis and mental health disorders: mechanisms, clinical evidence, and therapeutic implications

Mateusz Szabat^1♦, Klaudia Samuła², Dominika Ruszel², Emilia Goc², Julia Rogała², Katarzyna Markuszka², Kinga Polityńska², Martyna Sarzyńska², Sylwia Lepak², Zuzanna Irzyk²

¹Clinical Provincial Hospital No. 2 in Rzeszów, Poland.
²Faculty of Medicine, University of Rzeszów, Rzeszów, Poland.

^♦Corresponding author
Mateusz Szabat, Clinical Provincial Hospital No. 2 in Rzeszów, Poland

ABSTRACT

The microbiota-gut-brain axis is a bidirectional communication network connecting gastrointestinal function with the central nervous system. We summarize the growing literature on the effect of altered gut microbiota composition and microbial metabolite production on the development and course of mental health disorders and neurodegenerative diseases in this review. The therapeutic potential of microbe-targeted treatments for mental health disorders will also be evaluated. This review used selected peer-reviewed articles, including prospective cohort studies, randomized controlled trials, mechanistic studies, and systematic reviews examining the relationship between gut microbiota and mental health disorders. The epidemiology literature provides strong evidence for a consistent association between gastrointestinal disorders and an increased risk of various psychiatric and cognitive conditions. Emerging interventional research suggests that interventions that modify gut microbiota (i.e., psychobiotics) can have positive effects on depressive symptoms, and on certain aspects of stress-related cognition and some cognitive functions. In contrast, the size of these effects appears generally moderate and specific to the strain used in each intervention. Therefore, the cumulative evidence provides a biologically plausible link between gut microbiota and mental health disorders; however, the diversity of study designs, types of microbial interventions, and studied populations underscores the need for further wellcontrolled clinical trials that include microbial characterization of the participants’ microbiota, measurement of inflammatory biomarkers, and mechanistic outcomes to better define the therapeutic potential of interventions directed at modifying the microbiota.

Keywords: Brain–Gut Axis; Gastrointestinal Microbiome; Mental Disorders; Probiotics; Cognitive Dysfunction

Medical Science, 2026, 30, e111ms3861

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DOI: https://doi.org/10.54905/disssi.v30i172.e111ms3861

Published: 27 June 2026