These include alosetron, a selective serotonin receptor 3 (5-HT3R) antagonist that has previously been approved for the treatment of IBS-D (though carries a black box warning of ischemic colitis).205,206 Tegaserod, a selective serotonin receptor 4 (5-HT4R) agonist, has demonstrated efficacy in improving symptoms in IBS-C, including abdominal pain (though it had been temporarily withdrawn from the US market out of concern for potential adverse cardiovascular effects).207 Though constipation is less common in IBD populations, there is still analgesic potential in this setting. This evidence concerns the gene HTR4 and irritable bowel syndrome.