- Alter GI transit including laxatives, antispasmodics, 5-HT 3 antagonists (e.g. alosetron, ondansetron), 5-HT 4 agonists (e.g. tegaserod), triptans (5-HT 1B or 1D agonists), magnesium or aluminum-containing antacids, prokinetics, erythromycin, narcotics, anticholinergics, loperamide