Potential of Probiotics as Adjuvant Therapy to Reduce Depressive Disorder Based on Dose and Duration: A Meta-Analysis

Depression is a common and severe mood disorder affecting millions globally. Recent research suggests that probiotics may play a role in reducing symptoms of depression. Integrating probiotics into clinical practice can enhance patient outcomes, improve quality of life, and advance the overall care of individuals with depressive disorders. This meta-analysis aims to evaluate the effectiveness of probiotics as an adjunctive therapy for disorders. It focuses on determining the impact of probiotic dosage, duration, and specific strains on reducing depressive symptoms by modulating gut microbiota, which is implicated in the gut-brain axis and mental health. A systematic search on randomized controlled trials (RCTs) was conducted in PubMed, Scopus, and the Cochrane Library from 2019 to 2024, PRISMA guidelines for examining probiotics on depression. The selected studies met predefined inclusion criteria, including validated depression assessment scales. Data extraction involved a standardized form, and a meta-analysis was conducted using Rev 5.4 with a random-effects model to account for variations across studies. Our study showed that probiotics significantly reduce symptoms in patients with major depressive disorder (SMD = −0.37, 95% CI −0.64 to −0.10, p = 0.007) and in cases of mild to moderate depressive disorders (SMD = −0.75, 95% CI −0.17 to −0.33, p = 0.0004). A daily probiotic dose of 3×10⁹ CFU administered over 8-weeks was associated with a reduction in depressive symptoms, regardless of the initial severity of the condition. In individuals diagnosed with major depressive disorder (MDD), a higher dosage of 8×10⁹ CFU over the same duration yielded more pronounced therapeutic effects. These results contribute to the evidence supporting the role of the gut-brain axis in the pathophysiology of depression. They also highlight the potential of probiotics as adjunctive agents in depression management, thereby informing the development of evidence-based clinical guidelines for integrative treatment strategies. HIGHLIGHTS This study highlights that specific probiotics, dosages, and durations may reduce depressive symptoms. Clinicians should consider discussing probiotic options with patients and collaborating with other health workers to integrate this approach into comprehensive treatment plans. GRAPHICAL ABSTRACT