This prospective, open-label, randomized controlled clinical trial aims to evaluate the clinical efficacy and safety of Jingfang Granules in the treatment of diarrhea-predominant irritable bowel syndrome (IBS-D) with cold-dampness encumbering the spleen syndrome, and to explore its potential mechanisms of action. A total of 106 patients with IBS-D of cold-dampness encumbering the spleen syndrome are planned to be enrolled and randomly assigned to the experimental group and the control group, with 53 patients in each group. The treatment will last for 4 weeks, followed by a 12-week follow-up period. The primary outcome measure is the IBS Severity Scoring System (IBS-SSS). Secondary outcomes include the Traditional Chinese Medicine (TCM) syndrome score, the Bristol Stool Form Scale, patient-reported outcome (PRO) scales, the IBS Quality of Life (IBS-QOL) questionnaire, recurrence rate, and others. Exploratory measures, such as immune-inflammatory cytokines and biomarkers related to intestinal mucosal barrier function, will also be observed.

Inclusion Criteria:

1. Meet the Western medicine diagnostic criteria for diarrhea-predominant irritable bowel syndrome (IBS-D) (IBS symptoms lasting for at least 6 months, and meeting the Rome IV criteria in the past 3 months) and the traditional Chinese medicine diagnostic criteria for cold-dampness disturbing spleen syndrome;
2. Aged between 18 and 65 years, with no gender restriction;
3. Baseline IBS-SSS score ≥ 75;
4. No use of any medication for irritable bowel syndrome for at least 1 week before entering treatment;
5. Subjects are informed and voluntarily sign the informed consent form.

Exclusion Criteria:

1. Patients with severe cardiovascular, respiratory, liver, kidney, or other major organ diseases, diabetes, tumors, hematopoietic system disorders, nervous system diseases, or psychiatric disorders;
2. Patients with other organic digestive system diseases (e.g., peptic ulcer) or systemic diseases affecting gastrointestinal motility (e.g., hyperthyroidism, diabetes mellitus);
3. Patients currently using or requiring continuous use of medications that may affect gastrointestinal function (e.g., antidiarrheals, antidepressants, anxiolytics, intestinal microbiota regulators, antibiotics, etc.);
4. Patients who have taken antibiotics, steroids or other hormones, herbal preparations (including oral and intravenous), microecological preparations, or probiotics (such as yogurt) within the past 1 week;
5. Patients who have previously undergone abdominal or anorectal surgery;
6. Pregnant or breastfeeding women;
7. Patients with a history of allergy to relevant drugs or severe food allergy;
8. Patients who have participated in or are currently participating in other interventional clinical research studies within the past 3 months;
9. Patients who refuse to enroll in the observation or have other unstable factors, such as failure to take medication as prescribed, or taking other medications that affect the evaluation of efficacy, leading to inability to determine treatment effects, or incomplete data.