A Phase 2, Multi-center Study to Evaluate the Efficacy and Safety of ONO-2952 in Female Subjects With Diarrhea-Predominant Irritable Bowel Syndrome (IBS-D)

Inclusion Criteria: 1. Female 18-65 years of age (inclusive) 2. Diagnosed with IBS based on the following criteria (Rome III criteria): * Symptom onset at least 6 months prior to diagnosis, and * Recurrent abdominal pain or discomfort at least 3 days per month for the past 3 months, and * Abdominal discomfort or pain associated with two or more of the following at least 25% of the time: 1. Improvement with defecation 2. Onset associated with a change in frequency of stool/defecation 3. Onset associated with a change in form (appearance) of stool 3. Diagnosed with IBS-D, defined as loose/watery stools ≥ 25% and hard/lumpy stools ≤ 25% of defecations Exclusion Criteria: * Any structural abnormality of the gastrointestinal (GI) tract (other than esophagitis or gastritis) * History of Crohn's disease, ulcerative colitis, diabetes mellitus, lactose malabsorption, malabsorption syndromes, celiac sprue, or any upper GI symptoms that may impact the assessment of IBS symptoms