Inclusion Criteria:  Patients diagnosed with Irritable bowel syndrome using Rome III diagnostic criteria with Abdominal Pain/ Discomfort Intensity of weekly average of worst abdominal pain/ discomfort in past 24 hours score of ≥ 3.0 on a 0 to 10 point scale AND Stool Consistency of at least 2 days per week with at least one stool that has a consistency of Type 6 or Type 7 BSS or <3 CSBM per week Subject who can provide written informed consent and willingness to comply with the requirement of the protocol Able to communicate in English, Malay, or Mandarin languages  Exclusion Criteria:  Patients with known hypersensitivity or contraindication to Rifaximin Pregnant / breastfeeding women Patients who are on probiotics for the past 1 month Presence of family history of GI malignancy or alarm features suggested malignancy - e.g. Unintentional weight loss (≥ 10% of body weight in recent 6 months), GI bleeding History of gastrointestinal (GI) malignancy Patients with any hepatobiliary or pancreatic diseases Patients with severe depression, anxiety, or other psychological disorder Patients with any terminal disease Other conditions determined by the investigator to be inappropriate for this clinical study