Sodium picosulfate, magnesium oxide, and anhydrous citric acid is used in adults and children 9 years of age and older to empty the colon (large intestine, bowel) before a colonoscopy (examination of the inside of the colon to check for colon cancer and other abnormalities) so that the doctor will have a clear view of the walls of the colon. Sodium picosulfate is in a class of medications called stimulant laxatives. Magnesium oxide and anhydrous citric acid combine to form a medication called magnesium citrate. Magnesium citrate is in a class of medications called osmotic laxatives.