Loperamide, sold under the brand name Imodium, among others, is a medication used to decrease the frequency of diarrhea. It is often used for this purpose in inflammatory bowel disease and short bowel syndrome. It is not recommended for those with blood in the stool, mucus in the stool, or fevers. The medication is taken by mouth.

Common side effects include abdominal pain, constipation, sleepiness, vomiting, and a dry mouth. It may increase the risk of toxic megacolon. Loperamide's safety in pregnancy is unclear, but no evidence of harm has been found. It appears to be safe in breastfeeding. It is an opioid with no significant absorption from the gut and does not cross the blood–brain barrier when used at normal doses. It works by slowing the contractions of the intestines.

Loperamide was first made in 1969 and used medically in 1976. It is on the World Health Organization's List of Essential Medicines. Loperamide is available as a generic medication. In 2020, it was the 330th most commonly prescribed medication in the United States, with more than 700 thousand prescriptions.