Buckthorn (Frangula alnus or Rhamnus frangula) is a small, shrub-like tree in the alder family. The bark of these trees is used medicinally.
It is usually available as a powder of the dried bark.
Buckthorn bark has very mild laxative activity compared to other similar natural laxatives. As part of the famed "Hoxsey formula", buckthorn bark is also used in blood and system detoxification protocols. German Commission E has approved the use of the bark for constipation.