 Treatment: Patients who meet all entry criteria will be randomized 1:1:1 to one of three blinded treatment groups on Day 1 of the Treatment period. Patients will take an oral dose of study drug OD for 12 weeks and continue the daily electronic diaries BMs, rescue medication use, abdominal pain, and other symptoms. During treatment weeks 4, 8, and 12, patients will return to the clinic to undergo safety and efficacy assessments. 