Effect of Probiotic Supplementation on Gut Microbiota in Patients with Major Depressive Disorders: A Systematic Review

Systematic review of seven studies in adults with major depressive disorder across multiple countries. The evidence base included randomized controlled trials and one open-label trial assessing probiotic supplementation and gut microbiota-related outcomes.

Across the included studies, probiotic regimens varied by strain, product, and duration. One reported regimen used 2 g of freeze-dried multistrain probiotic powder twice daily, with a total cell count of 1 × 10^10 CFU/day; other interventions included L. plantarum PS128 capsules, a PROVIT multispecies probiotic drink, multistrain probiotic add-on therapy, Bifidobacterium breve CCFM1025 powder, and fermented milk containing Lacticaseibacillus paracasei Shirota.

Probiotic supplementation showed limited short-term effects on gut microbiota and only modest effects on depressive symptoms in major depressive disorder. Most studies did not find significant changes in gut microbiota composition after four to eight weeks of intervention. In Chahwan 2019, gut microbiota composition was similar across groups, although cognitive reactivity was significantly reduced in the probiotic group (p = 0.04). Overall, the evidence suggests possible small benefits but not a robust microbiome effect.

The evidence was limited by small study sizes, short intervention durations, and heterogeneous probiotic strains, formulations, and regimens. Most trials assessed outcomes only over four to eight weeks, and one study was open-label, which reduces confidence in the findings. More sensitive microbiome methods and longer, larger trials are needed.