In IBS patients with diarrhea, antidiarrheal agents such as loperamide and diphenoxylate can be effective in decreasing bowel movement frequency, improving stool form by enhancing intestinal water and ion absorption, and increasing anal sphincter tone at rest. These physiologic actions seem to explain the improvement in diarrhea, urgency, and fecal soiling observed in patients with IBS.
Loperamide (e.g.,Imodium, Pepto Diarrhea Control) is available over-the-counter. Diphenoxylate (e.g., Lomotil, Lomocot) is available by prescription. Diphenoxylate is potentially addictive.
These medications do not typically relieve abdominal pain and may cause constipation.
Source: Lembo T and Rink R. Current Pharmacologic Treatments of Irritable Bowel Syndrome. IFFGD Fact Sheet No. 168.