Probiotics to Prevent Relapse After Hospitalization for Bipolar Depression

Inclusion Criteria: * Age 18-65 (inclusive) * Capacity for written informed consent * Currently (or within the last 3 weeks) admitted to a Sheppard Pratt inpatient or day hospital program for symptoms of a depressive episode and a diagnosis Bipolar Disorder I or II, most recent episode depressed per Diagnostic and Statistical Manual of Mental Disorders 5th Edition (DSM-5), the diagnosis of which is confirmed with the Structured Clinical Interview for DSM-5 Disorders (SCID-5) * Proficient in the English language * Available to come to Sheppard Pratt Towson for study visits after hospital discharge Exclusion Criteria: * Depressive symptoms better accounted for by a diagnosis of Major Depressive Disorder, Schizoaffective disorder, Schizophrenia, or disorder(s) other than Bipolar Disorder I or II * DSM-5 diagnosis of intellectual disability or comparable diagnosis determined by previous version of the DSM * Substance- or medically-induced mood symptoms at time of Visit 1/Baseline visit * DSM-5 diagnosis of a moderate or severe substance use disorder, except for caffeine or tobacco, within three months prior to the Visit 1/Baseline visit * History of IV drug use * Any clinically significant or poorly controlled medical disorder as determined by the principal investigator and/or the study physician (e.g., HIV infection or other immunodeficiency condition, uncontrolled diabetes, congestive heart failure) * A serious medical condition that affects brain or cognitive functioning (e.g., epilepsy, serious head injury, concussion involving loss of consciousness, brain tumor, or other neurological disorder) * Pregnant, planning to become pregnant, or breastfeeding during the study period * Documented celiac disease * Participated in any investigational drug trial in the 30 days prior to the Visit 1/Baseline visit * Receipt of Electroconvulsive therapy (ECT) in the 30 days prior to the Visit 1/Baseline visit or planned ECT after hospital discharge