A study to verify the superiority of YM060 (ramosetron) to placebo for female patients with diarrhea-predominant irritable bowel syndrome (D-IBS) and to evaluate its safety.

Inclusion Criteria:

• Patients meeting the Rome III Diagnostic Criteria
• Loose (mushy) or watery stools within the last 3 months
• Abdominal discomfort and/or pain during their non-menstrual period

Exclusion Criteria:

• Patients with a history of surgical resection of the stomach, small intestine or large intestine
• Patients with a history or current diagnosis of inflammatory bowel disease (Crohn's disease or colitis ulcerative)
• Patients with a history or current diagnosis of colitis ischemic
• Patients with a current diagnosis of enteritis infectious
• Patients with a current diagnosis of hyperthyroidism or hypothyroidism
• Patients who are currently participating in another clinical trial (including a post-marketing clinical study) or those who participated in another clinical trial (including a post-marketing clinical study) within 12 weeks before the study
• Patients with a history or current diagnosis of malignant tumor
• Patients with a history of abuse of drugs or alcohol within 1 year or those who are currently abusing them