Effect of probiotic supplementation on schizophrenia symptoms and association with gastrointestinal functioning: a randomized, placebo-controlled trial.

OBJECTIVE: A range of immune system abnormalities have been associated with schizophrenia. Probiotic compounds modulate the immune response and offer a potential treatment strategy for schizophrenia. Probiotic compounds have also been observed to improve gastrointestinal dysfunction, which is a common problem in individuals with schizophrenia. We performed a randomized, double-blind, placebo-controlled trial to examine whether probiotic supplementation can reduce symptom severity in patients with schizophrenia receiving antipsychotic treatment and also whether probiotics are associated with bowel functioning. METHODS: Outpatients with schizophrenia (N = 65) meeting DSM-IV criteria and with at least moderately severe psychotic symptoms were enrolled in the study from December 2010-August 2012. Following a 2-week placebo run-in period, patients were randomly assigned to 14 weeks of double-blind adjunctive probiotic (combined Lactobacillus rhamnosus strain GG and Bifidobacterium animalis subsp. lactis strain Bb12) or placebo therapy. Psychiatric symptoms were assessed biweekly with the Positive and Negative Syndrome Scale (PANSS), and patients were queried weekly about their gastrointestinal functioning. RESULTS: Repeated-measures analysis of variance showed no significant differences in the PANSS total score between probiotic and placebo supplementation (F = 1.28, P = .25). However, patients in the probiotic group were less likely to develop severe bowel difficulty over the course of the trial (hazard ratio = 0.23; 95% CI, 0.09-0.61, P = .003). CONCLUSIONS: Probiotic supplementation may help prevent a common somatic symptom associated with schizophrenia. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT01242371.