The medicinal herb known as common buckthorn is a shrub originally native to northern Europe. It was later brought to the United States, where, in some areas, it has become an invasive pest. Not to be confused with the entirely different plant sea buckthorn, common buckthorn is an intensely active laxative. The berries and bark are the parts used medicinally.

Buckthorn is related to cascara sagrada ( Rhamnus purshiana), a milder laxative widely available in the US as an over-the-counter drug. Like cascara, as well as the OTC laxativesenna, buckthorn contains substances in the anthranoid family including anthraquinones, anthrones, and dianthrones. Anthroids work by slightly damaging the cells lining the colon.1 This in turn causes colon contraction, leading to bowel movements.

The fact that the laxative actions of anthroids involves cell damage has raised concerns that they might increase colon cancer risk. This does not appear to be the case; however, for a discussion of this controversial topic, see the Senna article.