To evaluate the efficacy and safety of TCM decoction Chang'an I Recipe in the treatment of IBS-D. A multicenter, randomized, double-blind, placebo-controlled clinical trial was designed. Patients were applied for central random number and were given corresponding treatment according to inclusion sequences.The treatment group was administered the Chang'an I Recipe, 150ml/bag, 3 times/day; while the control group was administered the placebo, 150ml/bag, 3 times/day. Both courses of treatment were 8 weeks.

Inclusion Criteria:

• Patients meeting the diagnostic criteria of Western medicine for IBS-D;
• aged 18-70 years old; with a baseline IBS-SSS score over 75 points;
• voluntarily signed the informed consent;
• local resident who could ensure follow-ups, with basic reading ability.

Exclusion Criteria:

• Patients with IBS-C, -M, and uncertain forms;
• accompanied with serious lesions in major organs including heart, liver, and kidney, hematopoietic system diseases, and tumors;
• gastrointestinal organic disease (e.g., chronic pancreatitis), or systemic diseases affecting the digestive tract motion (e.g., hyperthyroidism, diabetes, chronic renal insufficiency, and nervous system diseases);
• undergoing or requiring constant use of drugs that may affect gastrointestinal functions (e.g., anti-cholinergic drugs, calcium channel blockers, 5-HT3 receptor antagonist, antidiarrheal agents, antacids, prokinetic agents, antidepressants, anxiolytics, and intestinal flora regulating drugs);
• with history of abdominal surgery (e.g., cholecystectomy);
• with an allergy history of tested drugs or severe allergy history of food;
• pregnant and lactating female;
• with a history of neurological or psychiatric disorders;
• or participating in other clinical trial.