A psychobiotic approach to the treatment of depression: A systematic review and meta-analysis

[Display omitted] •Psychobiotics showed significant antidepressant-like effects for clinical depression.•Psychobiotics are advisable to be delivered in solid formulations.•Treatment using multiple-psychobiotic strains is superior to the single one.•Psychobiotics’ mood-regulating effects are age-dependent. A meta-analysis based on randomized controlled trials was conducted to clarify the effect of psychobiotics on depression in adults. The main result of concern is the score of the psychometric questionnaires. The outcomes were extracted using standardized mean difference (SMD) from each study, based on a random-effects model. Psychobiotic treatment results in a higher depression score reduction compared with the placebo. The observed SMDs ranged from −0.673 to 1.011, with most estimates being positive (63%). The estimated average SMD based on the random-effects model was 0.19 (95% confidence interval: 0.01–0.37), with the average outcome differed significantly from zero (Z = 2.018, P = 0.044). The subgroup analysis indicated that psychobiotics are advisable to be delivered in solid formulations with multiple probiotic strains and used in age-appropriate depressed patients. Collectively, psychobiotics showed great potential in managing mental health when appropriately administered.