The aim of this study is to evaluate the efficacy and safety of Changkang granule as compared to placebo over a 8-week treatment period and explore TCM syndrome types.

The clinical phase of the study comprises up to 2 weeks of screening for patient's eligibility, a 2-week run-in period , a 8-week double-blind treatment period, and a 4-week safety follow-up.

Patients report their IBS-related symptoms daily from run-in until end of treatment.

Inclusion Criteria:

1. The patients with diarrhea predominant irritable bowel syndrome (IBS-D) met Rome IV criteria;
2. It is in accordance with the syndrome differentiation standard of TCM, such as the syndrome of liver Qi multiplying spleen, spleen stomach weakness, spleen kidney yang deficiency or large intestine damp heat syndrome;
3. Male or female aged 18 to 65 years (including the boundary value);
4. The weekly mean NRS score of abdominal pain was ≥ 3.0, and the number of days with stool type 6 or 7 was more than 2 days per week;
5. IBS-SSS score>175;
6. Signed informed consent voluntarily.

Exclusion Criteria:

1. Patients with IBS-C、IBS-M or IBS-U；
2. Those who had been diagnosed with organic diseases of digestive system, such as inflammatory bowel disease, intestinal tuberculosis, intestinal tumor, etc., or still combined with peptic ulcer and infectious diarrhea;
3. Patients were diagnosed with similar symptoms of irritable bowel syndrome in the past, such as eosinophilic enteritis, collagen enteritis, lactose intolerance, etc;
4. Patients with non intestinal diseases of digestive system, such as tuberculous peritonitis, gallstones, liver cirrhosis, chronic pancreatitis, etc;
5. Previous diagnosis of systemic diseases affecting gastrointestinal function, such as hyperthyroidism or hypothyroidism, endometriosis, chronic renal insufficiency, autoimmune diseases, diabetes, etc
6. With history of abdominal surgery (e.g., cholecystectomy);
7. Patients with severe cardiovascular disease, liver, kidney and other major organ diseases, hematopoietic system diseases, tumor, nervous or mental system diseases (such as severe depression, severe anxiety)
8. Those who could not stop using concomitant drugs (prokinetic agents, anticholinergics, calcium channel blockers, 5-HT3 receptor antagonists, antidiarrheal agents, antacids, antidepressants, antianxiety drugs, intestinal flora regulators, etc.) that affected gastrointestinal motility and function ;
9. Taking emergency medication in the run-in period；
10. Pregnant or lactating women；
11. Those who are allergic to the test drug, emergency drug and its ingredients；
12. Suspected or confirmed history of alcohol and drug abuse;
13. Patients who participated in other clinical trials within one month before enrollment;
14. The researchers believe that others are not suitable for clinical trials.