This study tests CIN-103, a medicine, to see if it helps people with irritable bowel syndrome with diarrhea (IBS-D). IBS-D is a stomach problem causing pain and frequent loose stools. The study compares CIN-103 to a placebo, which looks like the real medicine but doesn't contain any active ingredients. By comparing both, researchers aim to find out if CIN-103 works better and is safe for patients.

Participants will have 8 visits over about 12 weeks. They need to take the study drug by mouth twice daily and complete daily diaries about their symptoms. A diary is like a journal where you write down how you feel. The researchers will use this information to see how well CIN-103 helps with stomach pain and stool consistency.

• Study lasts for about 12 weeks with 8 visits.
• You need to take the study pill twice a day.
• Participants record symptoms in a diary daily.

This study is only for adults 18 years or older who meet specific health conditions. Participants cannot have certain stomach or other health problems. If you want to join, you should not plan to change your diet or exercise too much during the study.