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Introduction: Evidence from randomized controlled trials investigating the effects of probiotics on depression published in the last four years has not yet been synthesized. The current systematic mini-review aimed to summarize the impact of probiotics in adults diagnosed with major depression with mild, moderate, or severe symptoms using studies published after May 2018.
Methods: A systematic literature search was conducted in PubMed, Web of Science, and Embase databases to identify randomized controlled trials that investigated the effect of any strain of probiotics alone or as an add-on therapy for the treatment of adult patients with mild, moderate, or severe symptoms of major depression and without other neurological and/or psychiatric disorders, published between May 2018 and August 2022. Data were extracted and qualitatively reviewed to determine the treatment effect. In addition, the quality of the methodology and risk of bias was assessed using the Cochrane risk-of-bias tool (RoB 2).
Results: Five studies met the inclusion criteria. All were randomized, parallel-group, placebo-controlled, double-anonymized trials with probiotics administered as an add-on therapy for treating mild and moderate symptoms of major depression only. In total, 303 patients (18–65 years) were randomized and treated with probiotics for 1–3 months. Four studies showed positive treatment effects, while one showed no difference between groups.
Discussion: There is encouraging evidence showing the potential beneficial effect of probiotics as an add-on treatment for patients with major depression with mild-to-moderate symptoms. However, future phase III trials are required to corroborate these results.