Racecadotril is an oral enkephalinase inhibitor used in the treatment of acute diarrhoea. It prevents the degradation of endogenous opioids (enkephalins), thereby reducing hypersecretion of water and electrolytes into the intestinal lumen. In a randomised double-blind study in 6 adult volunteers with castor oil-induced diarrhoea, racecadotril significantly reduced stool weight and stool number in comparison with placebo. Similar results have been obtained in treating castor oil-induced diarrhoea in rats. Racecadotril was significantly more effective than placebo in randomised double-blind studies in adults or children with diarrhoea (of infectious origin or in adults with HIV infection). In well controlled trials, racecadotril had efficacy similar to that of loperamide and was generally as effective as loperamide-oxide. Racecadotril had a similar tolerability profile to placebo, and was better tolerated than loperamide, in adults and children with diarrhoea. It caused significantly less constipation after resolution of diarrhoea than loperamide.