- 1) meet of diagnosis of IBS(ROME 4); 2) age of 18 to 65 years (inclusive); 3) IBS Symptom Severity Scale [17] (IBS-SSS) > 75 points (a range of 0-500 points of VAS on five questions) at baseline and during the 2-week run-in period; 4) Normal colonic evaluation (colonoscopy or barium enema) within 5 years; 5) Written informed consent.