Attapulgite is a magnesium aluminium phyllosilicate which occurs in a type of clay soil common to the Southeastern United States. When used in medicine, it physically binds to acids and toxic substances in the stomach and digestive tract. For that reason, it has often been used in antidiarrheal medications. Until 2003, it was the active ingredient used in Kaopectate, before that product was reformulated with bismuth subsalicylate.