Study of the Research Medicine CIN-103 in Adults with Irritable Bowel Syndrome with Predominant Diarrhea (IBS-D).

Are adult male and female subjects ≥ 18 years of age;

Have a body mass index between 18 and 45 kg/m2, inclusive at Screening;

Meet Rome IV Criteria for IBS-D by subject self-report of recurrent abdominalpain that is associated with ≥ 2 of the following over the last ≥ 6 months,with frequency of at least 1 day per week over the last 3 months (on average)before enrollment:

Related to defecation;

Associated with a change in frequency of stool; and/or

Associated with a change in form (appearance of stool).

Based on Investigator interview of subject's symptoms over the last 3 months,have ≥ 25% of bowel movements (BMs) with Bristol Stool Scale (BSS) Type 6 or 7 (loose or watery stools) and < 25% of BMs with BSS Type 1 or 2 (lumpy or hardstools) per the Rome IV Criteria for IBS-D;

In the opinion of the Investigator, are on a stable diet for ≥ 4 weeks prior toScreening and are not planning to change lifestyle, exercise, and/or diet thatmay impact symptoms of IBS-D during study participation;

Have a fecal calprotectin ≤ 100 mcg/g at the Screening Visit or Visit 2; Note:A single normal test result is adequate for study eligibility. If subjects arerescreened within 12 months, there is no need for repeat fecal calprotectinsample collection and testing. However, subjects who fail screening due to afecal calprotectin level > 100 mcg/g are not eligible for re-screening. Note:Repeat Fecal calprotectin may be considered with prior Sponsor approval.

Have a serum tTG-IgA (tissue transglutaminase immunoglobulin A) ≤ 4.99 FLU (fluorescent light units) at the Screening Visit;

Have undergone a colonoscopy examination within the designated time intervalprior to randomization, if they meet any of the following criteria. Note: Anegative Cologuard® test result is an acceptable alternative to colonoscopy forsubjects ≥ 45 years and at average risk for colon cancer.

Average risk, based on US Preventive Services Task Force RecommendationStatement for screening of colorectal cancer, with age ≥ 45 years (colonoscopy within 10 years or negative test results on Cologuard within 3 years);

Personal history of completely removed adenomatous colorectal polyps (colonoscopy within 5 years for polyps > 1 cm, within 10 years for polyps < 1 cm);

History of colorectal cancer or adenomatous polyps in a first-degreerelative before age 60 (colonoscopy within 5 years); or

History of colorectal cancer or adenomatous polyps in ≥ 2 first-degreerelatives at any age, or family history of hereditary colorectal cancer orpolyposis (colonoscopy within 5 years).

Have a diagnosis or suspected diagnosis of non-diarrhea predominant IBS (eg,IBS with a subtype of constipation, IBS with mixed or alternating bowel habits,un-subtyped IBS) or functional constipation by the Rome IV Criteria;

Non-infectious chronic lower gastrointestinal conditions including a history ofor current inflammatory bowel disease (ie, Crohn's disease, ulcerative colitis,indeterminate colitis), recurrent diverticulitis, microscopic colitis,lymphocytic colitis, celiac disease, non-celiac gluten sensitivity andnon-compliant on a gluten-free diet, untreated lactose intolerance, carcinoidsyndrome, Lynch syndrome, or familial polyposis, intestinal obstruction,stricture, toxic megacolon, solitary rectal ulcer syndrome, GI perforation,intra-abdominal or pelvic adhesions, ischemic colitis, radiation proctitis,chronic enteritis, non-infectious colitis, or impaired intestinal circulation (eg, aortoiliac disease);Note: Lactose intolerance and non-celiac gluten sensitivity will not exclude asubject from participation if the Investigator documents that the subject iscompliant on a special diet (lactose-free diet or gluten-free diet,respectively) and/or for lactose intolerance is successfully treated withcommercial lactase supplement(s).

Infectious lower gastrointestinal conditions requiring antibiotics ormicrobiome therapy; any microbiologically documented acute lowergastrointestinal colitis or enteritis requiring antibiotic treatment includingsuccessfully treated Clostridioides difficile colitis within 3 months prior toScreening, or a history of recurrent C. difficile colitis at any time in thepast;

Have a known family history of inflammatory bowel disease in at least 1first-degree relative;

Have a known history of a pelvic floor disorder associated with constipation (unless successful treatment has been documented by a normal balloon expulsiontest or anorectal manometry), refractory constipation not responsive tostandard medical therapy, fecal impaction that required hospitalization,cathartic colon, and/or active proctological condition;

Have a history of or current non-IBS chronic condition(s) with ongoing symptomsassociated with abdominal pain or GI discomfort (eg, gastroparesis, functionaldyspepsia, uncontrolled gastroesophageal reflux disease, polycystic kidneydisease, ovarian cysts, urological pain, or endometriosis);

Have a history of or current clinically significant arrhythmias as judged bythe Investigator, including ventricular tachycardia, ventricular fibrillation,and Torsades de pointes. Subjects with any abnormal electrocardiogram (ECG) notconsidered clinically significant by the Investigator are not excluded;

Have current or a history of diverticulitis, heme positive stool, orunexplained GI bleeding within 3 months prior to Screening.Note: Surgically repaired diverticulitis > 3 months prior to Screening ispermitted.

Have a history of surgical resection of the stomach, small, or large intestine;

Have had any major abdominal surgery within the 3 months prior to Screening;Note: Permitted procedures are uncomplicated appendectomy, cholecystectomy, andresection of benign polyps within the 3 months prior to Screening. Subjects whohad an appendectomy that was associated with any related complications orsequelae are eligible if the procedure was performed at least 6 months prior toScreening.

Are currently undergoing or planning to initiate treatment with weight lossmedication during study participation or prior weight loss surgery (eg, gastricbypass surgery, gastric banding);

Have a planned invasive elective surgery during the period of anticipated studyparticipation from the time of informed consent through the last study visit;