Ondansetron Works for Diarrhea-Predominant Irritable Bowel Syndrome

Ondansetron is a 5-hydroxytryptamine 3 receptor antagonist (5-HT3RA) used for the treatment of nausea and vomiting. 5-HT3RAs also cause constipation, and one of these agents, alosetron, is approved for the treatment of diarrhea-predominant irritable bowel syndrome (IBS-D).

To assess the efficacy of ondansetron in treating IBS-D, investigators randomized 120 patients to receive ondansetron (one to two 4-mg pills, two to three times daily, as titrated by the patient) or placebo for 5 weeks in a double-blind, crossover study.

After completing 5 weeks of treatment with ondansetron or placebo, patients underwent a 2–3 week washout period, followed by 5 weeks of the alternate treatment. The primary endpoint was average stool consistency during the …