Tehran University of Medical Sciences Iranian Journal of Psychiatry 1735-4587 15 1 2020 02 10 10 16 Mahin Eslami Shahrbabaki Neurology Research Center, Psychiatry Department of Shahid Beheshti Hospital, Afzalipour Medicine School, Kerman University of Medical Sciences, Kerman, Iran. Saleheh Sabouri Pharmaceutics Research Center, Institute of Neuropharmacology, Kerman University of Medical Sciences, Kerman, Iran. Abdolreza Sabahi euroscience Research Center and Institute of Neuropharmacology, Psychiatry Department of Shahid Beheshti Hospital, Afzalipour Medicine School, Kerman University of Medical Sciences, Kerman, Iran. Delaram Barfeh Neurology Research Center, Afzalipour Medicine School, Kerman University of Medical Sciences, Kerman, Iran. Parisa Divsalar Neuroscience Research Center and Institute of Neuropharmacology, Psychiatry Department of Shahid Beheshti Hospital, Afzalipour Medicine School, Kerman University of Medical Sciences, Kerman, Iran. Mahdi Esmailzadeh Psychiatry Department of Shahid Beheshti Hospital, Neurology Research Center, Afzalipour Medicine School, Kerman University of Medical Sciences, Kerman, Iran. Atefeh Ahmadi Nursing Research Center, School of Nursing and Midwifery, Kerman University of Medical Sciences, Kerman, Iran. 2019 06 16 Objective: Bipolar disorders are among the most common chronic mental disorders. Despite the recent improvement in controlling psychiatric disorders, treatment of bipolar disorders remains a challenge. The aim of this study was to determine the effect of consuming probiotics in patients with bipolar disorder-type 1 compared to the placebo group. Method: This was a permuted blocked randomized clinical trial conducted in Shahid Beheshti mental hospital in Kerman, Iran, from October 2017 to October 2018. Two psychiatrists diagnosed and hospitalized all 38 patients with type 1 bipolar disorder based on the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). Using blind randomized blocking method size 4, patients were divided into 2 groups of placebo and probiotic. Young Mania Rating Scale (YMRS) and Hamilton's Depression Rating Scale (HDRS) were completed at the beginning, week 4, and week 8 of the study by a psychiatry resident. Independent t test, Mann-Whitney and repeated measures ANOVA tests were used. Data were analyzed using SPSS software version 20. Results: There was no significant difference between the 2 groups in age, sex, and severity of mania and depression. Consumption of probiotics reduced the scores of YMRS and HDRS over time in the probiotic group more than the placebo group, but it was not significant. Conclusion: Consumption of probiotics had non-significant effects on improvement and treatment of bipolar type 1 patients. It is suggested that future studies be conducted with different probiotic microbial strains and longer period of treatment. https://ijps.tums.ac.ir/index.php/ijps/article/view/1814 https://ijps.tums.ac.ir/index.php/ijps/article/download/1814/898