Because the study sponsor chose to discontinue funding for this protocol following a change in leadership, the study was terminated early.

The purpose of this study is to determine the safety and effectiveness of a nutritional supplement, the probiotic bacteria GanedenBC30. Probiotics are live microorganisms which when taken in large enough amounts are supposed to provide a health benefit. The investigators would like to see whether this supplement can be used as a treatment for Irritable Bowel Syndrome (IBS) and Major Depressive Disorder (MDD). Participants in the study will have both IBS and MDD. In order to find out if GanedenBC30 is effective in treating IBS and MDD, the investigators will compare it to a placebo. About 32 people will take part in this research study. About half of these 32 people will take part at Charles River Medical Associates and half will take part at Burlington Medical Associates. Participants will be recruited from among patients already being seen at Charles River Medical Associates or Burlington Medical Associates for their primary care. The study will last for two months, during which time participants will make eight study visits and will take either Ganeden BC30 or placebo. The investigators hypothesize that subjects treated with the probiotic will have significantly better outcomes with regard to depression and IBS symptoms compared to those who receive placebo.

Inclusion Criteria:

• Able to give Informed Consent
• Meet criteria for Irritable Bowel Syndrome
• Meet criteria for Major Depressive Disorder
• Men and women ages 18 to 65
• Women of childbearing potential must be using an adequate methods of contraception
• Can be on an antidepressant medications, but must have been on the medication for at least 8 weeks and at a stable dose for 4 weeks
• Can be on medications for IBS, but must have been on medications for at least 8 weeks and at a stable dose for 4 weeks

Exclusion Criteria:

• Patients who have failed one or more trials of probiotics for IBS
• Patients who report an inadequate response to less than two or more than four adequate trails of antidepressant treatments during the current depressive episode at a therapeutic dose for an adequate duration
• Women who are pregnant or breastfeeding
• Patients with "alarm signs" or "red flags" as defined by American Gastroenterological Association (AGA) are excluded [6], unless they have been fully evaluated to rule out other significant diseases.
• Patients with known diagnoses of digestive organic disease, celiac disease and lactose intolerance prior to the screening.
• Patients who report an inadequate response (less than 50% decrease in depressive symptom severity) to less than two or more than four prior adequate trials of antidepressant treatments during the current depressive episode (including monotherapy treatment and distinct combination regimens) at a therapeutic dose (as defined by the MGH-ATRQ) and for an adequate duration (minimum six weeks for any monotherapy).
• Patients who report treatment with adjunctive medications to their antidepressant for a minimum of four weeks during the current depressive episode.
• Patients with a current need for involuntary commitment or who have been hospitalized within four weeks of the Screening Visit for the current major depressive episode.
• Patients who have received ECT during the current episode.
• Patients who have a current Axis I diagnosis of:

Delirium, dementia, amnestic, or other cognitive disorder; Schizophrenia or other psychotic disorder, based on the PDSQ; Bipolar I or II disorder, based on the PDSQ; Patients with a clinically significant Axis II (DSM-IV-TR) diagnosis of borderline, antisocial, paranoid, schizoid, schizotypal or histrionic personality disorder.

• Patients experiencing hallucinations, delusions, or any psychotic symptomatology in the current depressive episode.
• Patients who have met DSM-IV-TR criteria for any significant substance use disorder within the past six months, based on the PDSQ.
• Patients receiving new onset depression-focused psychotherapy within 6 weeks of screening, or at any time during participation in the trial.
• Patients who have been previously randomized in a probiotics clinical trial (lifetime).
• Patients who have participated in any clinical trial with an investigational drug or device within the past month.
• Patients who, in the opinion of the investigator, are actively suicidal or homicidal and at significant risk for suicide or homicide.