The objective of this study is to explore efficacy, safety and tolerability 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