Could a daily probiotic help tame schizophrenia?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Age 18-65, inclusive. * Capacity for written informed consent. * Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) diagnosis of schizophrenia or schizoaffective disorder (APA 2013) as determined by the Structured Clinical Interview for DSM-5 Disorders (SCID-5). * Outpatient at the time of enrollment. * Residual psychotic symptoms of at least moderate severity as evidenced by a Positive and Negative Syndrome Scale (Kay et al., 1987) (PANSS) total score of 60 or higher AND one or more of the following: one or more PANSS positive symptom scores of 4 or higher; OR containing at least three positive or negative items with scores of 3 or higher at the screening visit. * Receiving antipsychotic medication for at least 8 weeks prior to starting the study with no medication changes within the previous 21 days. * Proficient in the English language. Exclusion Criteria: * DSM-5 diagnosis of intellectual disability or comparable diagnosis determined by previous versions of the DSM. * Any clinically significant or unstable medical disorder as determined by the investigators, including congestive heart failure, liver disease, renal failure, any diagnosis of cancer undergoing active treatment. * A primary immunodeficiency condition such as HIV infection, or undergoing cancer chemotherapy, or receiving systemic corticosteroids, methotrexate or monoclonal antibodies for treatment of an autoimmune disorder. * History of IV drug use. * DSM-5 diagnosis of a moderate or severe substance use disorder, except for caffeine or tobacco, within the last three months prior to the screening visit. If the patient has a positive drug toxicity screen at the time of visit 1 (screening) further evaluation by the investigator will be done of the substance use to determine eligibility. * Participated in any investigational drug trial in the past 30 days. * Pregnant or planning to become pregnant during the study period. * Receipt of antibiotic medication within the 14 days prior to visit 2 (as anaerobic organisms residing in the gastrointestinal tract may be minimally affected by antibiotics). Of note, patients on antibiotic may be re-screened once the minimum duration of time since antibiotics use has been met. * Current and regular use of a probiotic and or prebiotic supplement within the past 2 weeks. Of note, patients taking prebiotic or probiotic supplements may be re-screened. * Documented inflammatory bowel disease (e.g. Crohn's disease or ulcerative colitis) or celiac disease