Diphenoxylate (R-1132) is an opioid agonist used for the treatment of diarrhea that acts by slowing intestinal contractions and peristalsis allowing the body to consolidate intestinal contents and prolong transit time, thus allowing the intestines to draw moisture out of them at a normal or higher rate and therefore stop the formation of loose and liquid stools. It is the main active ingredient in the anti-peristaltic medication Lomotil, which also contains atropine as noted below.
Diphenoxylate is the prototype of a small subfamily of opioids including difenoxin (diphenoxylic acid) (an active metabolite of diphenoxylate produced in the human body) and loperamide (which unlike the other two work exclusively in the intestines because it does not cross the blood–brain barrier). It was discovered at Janssen Pharmaceutica in 1956. It is a congener to the narcotic pethidine of which the common brand names are Dolantin and Demerol amongst others. Other somewhat more distant relatives include alphaprodine (Nisentil) and piritramide (Dipidolor).