Investigations on drug produced and subjectively experienced discriminative stimuli. 2. Loperamide, an antidiarrheal devoid of narcotic cue producing actions.

By means of a new behavioral procedure effectively controlling the narcotic stimulus properties of drugs, it was found that the oral administration of fentanyl, morphine, codeine and diphenoxylate produced the narcotic cue. The new antidiarrheal loperamide did not produce this cue in rats as sensitive as being able to detect 0.005 mg/kg s.c. fentanyl. The results are discussed in terms of drug abuse liability.