This is a randomized controlled trial to explore the efficacy and safety of CMTS4520 (Dietary Fiber Probiotics) for patients with chronic diarrhoea.

At least 100 subjects who meet all the inclusion criteria but do not meet any exclusion criteria will be enrolled in this study. They will be randomly assigned to the CMTS4520 group (dietary fiber probiotics capsules) and the control group (placebo). Data of demographic characteristics, intestinal symptoms, medicine treatment usage and clinical outcomes will be collected. After treatment, they will enter the follow-up period for efficacy and safety evaluation.

Inclusion Criteria:

Meet all of the following inclusion criteria :

1. Voluntary sign informed consent, age 18-70 years old (including the threshold), male and female.

2. Using the Rome IV criteria as the diagnostic criteria:

   1. Defecation frequency is greater than or equal to 3 times per day or significantly exceeds the usual habit, with a disease duration of > 4 weeks, or recurrent diarrhea with an intermittent period within 2 - 4 weeks;
   2. Loose stools: Types 5, 6, and 7 based on the Bristol Stool Form Scale.

3. The subject or his/her legal representative has given informed consent, is fully aware of the purpose of the study, is able to communicate well with the investigator, and is able to understand and comply with the requirements of the study.

Exclusion Criteria:

All exclusion criteria below are not met:

1. Participants with a history of intestinal resection.

2. Participants with organic lesions of the digestive tract (e.g., tumor, inflammation, anal fissures, Crohn's disease, ulcerative colitis, radiation enteritis, intestinal adhesions, intestinal tuberculosis) as confirmed by colonoscopy within the past 24 months.

3. Participants with diarrhoea secondary to systemic diseases affecting the digestive tract, including:

   1. Neurological diseases (e.g., Parkinson's disease, spinal cord injury, multiple sclerosis).
   2. Muscle diseases (e.g., amyloidosis, dermatomyositis).
   3. Psychiatric disorders or severe mood disorders (e.g., A Hospital Anxiety and Depression Scale score ≥15).
   4. Opioid-induced diarrhoea.
   5. Poorly controlled metabolic diseases (e.g., thyroid dysfunction) or metabolic diseases with gastrointestinal complications (e.g., gastrointestinal autonomic dysfunction, diabetic gastroparesis).

4. Diarrhea secondary to intestinal infectious diseases, including but not limited to Clostridioides difficile infection, chronic bacillary dysentery, intestinal tuberculosis, and parasitic infection-induced diarrhea.

5. Have a history of major surgery or severe trauma within 3 months and have not fully recovered.

6. Participants with any of the following cardiac abnormalities:

   1. New York Heart Association (NYHA) Class III or higher heart failure.
   2. Myocardial infarction or unstable angina within the past 6 months.
   3. Prolonged QTc interval on electrocardiogram (≥450ms for males, ≥470ms for females).
   4. Atrial arrhythmias that cannot be stably controlled by drugs and ventricular arrhythmias requiring pharmacological control (including grade 2 or higher atrioventricular block).

7. Participants with poor lung function, as assessed by the investigator, that may impact study treatment, such as acute chronic obstructive pulmonary disease(COPD) or those requring long-term oral, intravenous corticosteroids (excluding inhalant/spray formulations).

8. Uncontrolled immune diseases requring long-term systemic corticosteroid use (excluding topical use).

9. Participants with reproductive system disorders that may cause abdominal pain (e.g., ovarian cysts, endometriosis, primary dysmenorrhea).

10. Participants with significant laboratory abnormalities that, in the investigator's judgment, may affect safety or study completion, including:

    1. Hemoglobin <100g/L.
    2. Serum creatinine ≥1.5 times the upper limit of normal (ULN).
    3. Abnormal liver function (AST>1.5×ULN, ALT>1.5×ULN or total bilirubin >1.5×ULN).
    4. Clinically significant abnormalitieshe in routine stool tests or fecal occult blood indicating gastrointestinal lesions.

11. Participants with active hepatitis (requiring or undergoing long-term treatment), HIV, or active tuberculosis.

12. Participants with a history of drug or alcohol abuse (defined as consuming more than 14 standard drinks peer week: 1 standard drink= 360mL of beer, 45mL of 40% spirits, or 150mL of wine) or substance abuse.

13. Participants with known allergies or intolerances to the investigational drug, similar drugs or excipients.

14. Participants who have used anti-infective drugs (antibiotics, antifungals, antivirals) within 14 days prior to enrollment or require anti-infective treatment at the time of enrollment evaluation.

15. Participants who have used drugs or foods that regulate gut microbiota (e.g., bifidobacterium, probiotics, prebiotics, fermented milk, yogurt) within 2 weeks prior to screening or during the study.

16. Women who are pregnant, breastfeeding, or unwilling to use effective contraception for 3 months after the last dose of the study drug.

17. Participants who have participated in drug intervention clinical trials within 1 month prior to enrollment.

18. Any other condition that, in the investigator's judgment, makes the participant unsuitable for the study.