- Medications that alter GI transit including laxatives, magnesium and aluminum containing antacids, prokinetics, erythromycin, narcotics, aspirin, anti-cholinergics, tricyclic antidepressants, SNRI and newer antidepressants. With the exception of GoLYTELY which will be taken the evening prior to colon study day. 4- Selective serotonin reuptake inhibitor (SSRI) antidepressants are permissible at low, stable doses. All medications shall be reviewed and dis/approved by the principal investigator on a case by case basis.