Irritable bowel syndrome with diarrhea (IBS-D) is a functional gastrointestinal disorder, with characteristics of defecation related abdominal pain and diarrhea. Routine treatment strategy for IBS-D is symptom-based with unsatisfactory results, while there is a growing interest in complementary and alternative medicine such as Traditional Chinese Medicine. However, lack of high-quality evidences being the obstacle for its development.

This study aims to evaluate the efficacy of Fengliao Changweikang Keli (FLCWK) on symptoms and health-related quality of life in mild to moderate IBS-D patients.

After 2-week run-in period, each participant will be randomized to a sequence of six 4-week double-blind treatment periods of FLCWK 8 g three times daily or placebo, separated by 2-week washout periods.

Inclusion Criteria:

1. Aged between 18 and 75 years.
2. Mild to moderate IBS-D patients, with IBS Severity Scoring System (IBS-SSS) scores of 75 to 300 points[14].
3. Ability to complete questionnaires and provide written informed consent.
4. Current use of IBS medications (probiotics, antibiotics, antispasmodic, antidiarrheal and neuromodulators) should be prescribed on a stable dose at least 30 days prior to enrollment, and have no plan to change the dose, diet or lifestyle.
5. Normal blood cell count, liver function, creatinine and urea levels within the last 2 weeks.

Exclusion Criteria:

1. History of organic gastrointestinal diseases such as inflammatory bowel disease, celiac disease and malignancy.
2. Scores of IBS-SSS > 300 points or IBS-SSS < 75 points.
3. History of severe heart, kidney or liver diseases.
4. Pregnant or breastfeeding.
5. Current alcohol or drug abuse.