A review on the effect of Probiotic Supplementation on Anxiety and Stress Levels

Abstract

Anxiety and stress show a crucial global psychological burden that needs effective clinically management ways. The purpose of this article review is to quantitatively evaluate the effectiveness of probiotic supplementation in lowering anxiety and stress scores in human clinical trials. PubMed/Medline, Scopus, Frontier, and Google Scholar were systemically queried for studies of this topic that were published from 2017 until 2025. The randomized controlled trials (RCT) and a double-blind, placebo-controlled trial that was written in English were included. The specific combinations of MeSH terms and keywords was used to search the studies of this topic. The current review summarized clinical evidence of thirty-five randomized and non-randomized trials in the study of the impact of probiotic supplementation on anxiety and stress levels. In general, about two-thirds (23 out of 35) of the studies indicated a positive outcome of probiotics on at least one stress or anxiety-related outcome and a third (12 studies) showed no significant effect after the administration of probiotics. These results imply that probiotics can have small psychological advantages, especially to people with mild to moderate stress or subclinical anxiety. The current review summarised clinical evidence of thirty-five studies examining the effects of probiotic supplementation on anxiety and stress levels. Most studies showed some small-scale positive changes in subjective stress, trait anxiety, mood reactivity or other facets of psychological outcomes, especially in those with mild to moderate symptoms. Altogether, it can be concluded that existing literature indicates that probiotics can bring about some small-yet-significant effects on stress and anxiety, but the evidence is still not conclusive. Future research should therefore aim at identifying distinct mechanistic pathways, identifying the best strains, dosage, and duration.