Effect of Supplementation with Probiotics in Patients with Schizophrenia: Systematic Review and Meta-Analysis of Randomized Controlled Clinical Trials

Supplementation with probiotics seems to confer protective effects in individuals with schizophrenia (SZ), although available results are inconclusive. The aim of this study was to systematically review existing randomized clinical trials (RCTs) to critically assess the effect of probiotics on psychiatric symptoms, anthropometric indicators, lipid profiles, glycemic indices, inflammation, and oxidative stress in adults with SZ. A systematic search was conducted in four databases from inception until January 2025. Six RCTs were included in the quantitative analysis that demonstrated beneficial effects of probiotics on SZ severity determined via the Positive and Negative Syndrome Scale (PANSS), with significant reductions in PANSS (MD = −0.50, p = 0.001), PANSS Negative (MD = −0.31, p = 0.050), and PANSS General scores (MD = −0.33, p = 0.036), alongside reductions in body weight (MD = −0.92, p = 0.000), body mass index (MD = −0.53, p = 0.016), and total cholesterol (SMD = −0.34, p = 0.005). Furthermore, probiotic interventions reduced baseline glucose (SMD = −0.59, p = 0.000), insulin (MD = −0.68, p = 0.000), and measures of insulin sensitivity/resistance and significantly improved biomarkers of inflammation and oxidative stress. To summarize, this meta-analysis suggests that probiotics may confer beneficial effects in patients with SZ through improving psychiatric symptoms as well as markers of body weight, lipid and glucose metabolism, inflammation, and oxidative stress.