AbstractClonidine, lidamidine, and loperamide each inhibited castor oil‐induced diarrhea in the rat. Clonidine and lidamidine, but not loperamide, also induced diuresis but at doeses above those producing antidiarrheal activity. Clonidine and lidamidine, but not loperamide, produced autonomic and central effects including piloerection, hypotonia, exopthalmus and ataxia at doeses similar to those producing antidiarrheal activity. These data suggest that only loperamide possesses selective antidiarrheal activit