Peppers are common food ingredients used worldwide. They are also added in traditional antidiarrhoeal formulations of different herbs. Piperine (1) is an alkaloidal constituent of black and long peppers recently established as a bioavailability enhancer of drugs and other substances. As a part of efforts to study its effects on the gastrointestinal tract, the experiments were performed to determine the rationale, if any, for its use in traditional antidiarrhoeal formulations. Antidiarrhoeal activity of 1 against castor oil, MgSO4 and arachidonic acid was studied in mice. It significantly inhibited diarrhoea produced by these cathartics at 8 and 32 mg/kg p.o. dose. Inhibition of castor oil induced enteropooling by 1 suggests its inhibitory effect on prostaglandins. The results validate the rationale for its use in traditional antidiarrhoeal formulations.