Loperamide is an over-the-counter (OTC) antidiarrheal sold under the brand name Imodium, among others. Loperamide is an opioid-receptor agonist and acts on the u-opioid receptors in the myenteric plexus in the large intestine. It is an opioid with no significant absorption from the gut and does not cross the blood brain barrier when used at normal doses.