Dose Escalation Trial of Traditional Chinese Medicine for Irritable Bowel Syndrome (TCM- IBS)

Inclusion Criteria: * Age 18- 75 * All IBS patients attending the Gastroenterology Clinic of the Prince Of Wales Hospital of Hong Kong. * IBS diagnosed by Rome III criteria: * Recurrent abdominal pain or discomfort at least three days per month in the previous three months * Symptoms onset at least six months prior to diagnose * Pain or discomfort associated with two or more of the following: 1. Improvement with defecation 2. Onset associated with change in frequency of stool 3. Onset associated with a change in form (appearance) of stool * Normal colonic evaluation (colonoscopy or barium enema) in past 5 years * No "global symptom improvement" as rated by patients (see below) at screening and during the two- week run- in period to baseline * Normal full blood count, liver function test and renal function test. * Informed written consent for participation into study. * Ethical approval will be obtained from the Joint CUHK-NTEC Clinical Research Ethics Committee as well as the IRB of UMB. Exclusion Criteria: * Past or present history of organic disease of gastrointestinal tract (e.g. colorectal cancer, advanced colonic polyp, celiac disease, inflammatory bowel disease, peptic ulcer and previous gastrointestinal surgery). (Note: those with polyps removed during colonoscopy can be included, as long as no known polyps remained. * Systemic diseases that cause diarrhea or constipation (e.g. thyroid disease, diabetic neuropathy) * Lactose intolerance * Severe liver disease (e.g. cirrhosis, chronic active hepatitis) * Renal impairment (serum creatinine level \> 150mmol/L) * Women who are pregnant, lactating or not practicing proper contraception * Known hypersensitivity to herbal medicine * Concommitant use of prescription antidepressant medication * Current alcoholism and drug use * Current psychiatric illness or dementia * Fever or severe illness at baseline (week 0).