This is a A Multicenter, Randomized, Double-blind, Placebo-controlled, Clinical Trial to Evaluate the Efficacy and Safety of Different Doses of OPS-2071 in the Treatment of Irritable Bowel Syndrome of Diarrhea type (IBS-D).The trial is mainly divided into three periods: screening period, treatment period and follow-up period.

Screening period:

After signing the Informed Consent Form, subjects entered a 14-day screening period to evaluate inclusion/exclusion criteria and collect demographic information, medical history, etc. Subject's previous medication should be eluted and concomitant medications should be prohibited.

Treatment period:

After the screening period, subjects who meet the inclusion criteria and do not meet the exclusion criteria will be randomly assigned (1:1:1:1) to four treatment groups to receive a 2-week treatment period. Weekly follow-up and relevant examinations will be performed.

Follow-up period:

The safety follow-up visit will be conducted by telephone on Day14 (+2) after the last dose.

Inclusion Criteria:

1. Subjects who are able to fully understand and willing to comply with the trial procedures, and voluntarily participate in the trial and sign the Informed Consent Form;
2. Subjects aged 18 to 65 years at the time of ICF signing;
3. Subjects who meet Rome IV diagnostic criteria for IBS-D;
4. The following criteria should be met during the screening period:

Exclusion Criteria:

1. Subjects who have gastrointestinal alarm symptoms within 14 days before screening, such as hematochezia, positive fecal occult blood test, anemia, abdominal mass, ascites, fever, unexplained body mass loss, and nocturnal diarrhea;
2. Subjects with previously confirmed diagnosis of digestive organic diseases, such as inflammatory bowel disease, intestinal tuberculosis, intestinal polyps (except for polyps ≤ 0. 3 cm or polypectomy time ≥ 15 days), intestinal diverticulum, intestinal tumor, etc., or patients still complicated with peptic ulcer and infectious diarrhea;
3. Subjects with previously confirmed diagnosis of diseases affecting digestive system function, such as uncontrolled hyperthyroidism or hypothyroidism, chronic renal failure, autoimmune diseases, diabetes, and neurological (such as anorexia nervosa) or serious psychiatric system diseases (such as major depression or severe anxiety);
4. Subjects with previously confirmed diagnosis of diseases with symptoms similar to IBS, such as eosinophilic enteritis, microscopic colitis (including collagenous colitis and lymphocytic colitis), lactose intolerance, malabsorption syndrome, etc.;
5. Subjects with previously confirmed diagnosis of non-intestinal digestive diseases, such as tuberculous peritonitis, gallstones, cirrhosis, chronic pancreatitis, etc.;