 ScreeningBaseline: Patients will undergo an up to 28-day ScreeningBaseline period to allow for any necessary diagnostic procedures, allow for required washout of medications and to determine study eligibility. If otherwise eligible based on screening criteria, patients will undergo a 2-week baseline assessment using an electronic diary where they will record daily assessments of bowel movements BMs, stool consistency Bristol Stool Form Scale-BSFS, abdominal pain and other IBS-related symptoms. Data from the two-week electronic diary assessment just prior to the randomization visit will be used to confirm IBS-C and study eligibility as well as define the patients baseline from which change will be determined. 