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 laxative senna, 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.
Although buckthorn works in much the same manner as senna and cascara, its effects are stronger (sometimes unpleasantly so), and it is also more likely to cause nausea. In Europe, it nonetheless continues to be marketed as an approved laxative. In the US, it is not used in OTC products.
A typical dose of buckthorn provides 20-30 mg of anthrones, often measured in the form of glucofrangulin A. Like cascara and senna, it is usually taken at bedtime with the intention of producing a bowel movement in the morning.
Buckthorn must be allowed to dry for several months before it is taken internally. This drying process reduces levels of tannins and other irritants that would otherwise almost certainly cause severe nausea.
As noted above, buckthorn may cause nausea or vomiting. It may also cause a harmless red or yellow discoloration of the urine. Buckthorn is not recommended for long-term use because, like all stimulant laxatives, this may induce dependency.
People with significant colonic disease, such as ulcerative colitis, should not use buckthorn. (This, too, is common to all stimulant laxatives.)
If buckthorn is repeatedly taken to the point of diarrhea, the body may become depleted of the mineral potassium. This is particularly dangerous for people using drugs in the digoxin family; dangerous cardiac arrhythmias may occur if potassium levels are allowed to become inadequate. People who additionally use medications that deplete the body of potassium, such as thiazide or loop diuretics, are at special risk of this complication of buckthorn overuse.
Safety in pregnant or nursing women, young children, or people with severe liver or kidney disease has not been established.