Among the medications generally used to affect gut physiology or abdominal pain are antispasmodics, tricyclic antidepressants (TCAs), loperamide, Cholestyramine (for patients with cholecystectomy or who may have idiopathic bile acid malabsorption) and serotonergic agents (5-HT3 receptor antagonists and 5-HT4 receptor agonists). These agents show relative success in improving individual symptoms only, and are only effective in specific subgroups of patients (e.g.- for diarrhea-predominant, but not constipation-predominant IBS, or visa versa). Due to the heterogeneity of IBS, an effective therapy for one may often lead to deterioration in another. For example, Alosetron, an extensively studied 5-HT3 antagonist which has shown statistically significant improvement in women with diarrhea-predominant IBS, causes constipation in 20-30% of patients, and there has been no clear evidence of a benefit for men.