The investigators intend to explore the hypothesis that symptoms of schizophrenia may be reduced by the administration of a probiotic supplement when used in addition to standard antipsychotic medications.

The primary aim of the current study is:

1. To evaluate the safety and efficacy of a supplemental probiotic therapy, containing the microorganisms Lactobacillus rhamnosus GG and Bifidobacterium lanimalis subsp. lactis (BB12), for individuals with schizophrenia who have residual psychotic symptoms of at least moderate severity.

   Secondary aims of the study are:

2. To assess the effect of probiotic treatment on patients' gastrointestinal functioning

3. To study the effect of probiotic treatment in lowering the levels of antibodies to casein and gliadin.

4. To investigate the association between the efficacy of probiotic therapy and initial levels of antibodies to gliadin and casein.

Inclusion Criteria:

• Age 18-65.
• Capacity for written informed consent.
• Primary Axis I diagnosis (DSM-IV) of schizophrenia, any type, OR schizoaffective disorder (APA, 1994).
• Currently an outpatient at the time of enrollment.
• Residual psychotic symptoms which are at least moderately severe as evidenced by one or more PANSS positive symptom scores, and/or PANSS negative symptom scores of 4 or more; OR a total PANSS score of 50 or more, containing at least three positive or negative items with scores of 3 or more at screening.
• Conformance to PORT Treatment Recommendation re Maintenance Antipsychotic Medication Dose (Buchanan et al., 2010).
• 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:

• Diagnosis of mental retardation.
• Any clinically significant or unstable medical disorder as determined by the investigators, including congestive heart failure, abnormal liver function or disease, renal failure, acute pancreatitis, any diagnosis of cancer undergoing active treatment, HIV infection or other immunodeficiency condition.
• History of IV drug use.
• Primary diagnosis of substance abuse or dependence according to DSM-IV criteria within the last three months.
• 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 previous 14 days (as anaerobic organisms residing in the gastrointestinal tract may be minimally affected by antibiotics).
• Documented celiac disease (as such persons should be on a gluten-free diet as this is the standard care).
• Of note, the investigators are not limiting the study to individuals with elevated levels of gliadin or casein antibodies as the investigators intend to look at these levels as a predictor of response.

Adverse events were collected over a 16 week period, including the 2 week placebo run in and the 14 week double-blind treatment phase.

Did not perform more detailed measures of gastrointestinal functioning or obtain a more complete history of participants' gastrointestinal symptoms and associated treatment