Buckthorn bark has been used medicinally since at least the 1600s, when it was listed in a primary medical reference called the London Pharmacopeia. Although most herbs have had a wide variety of traditional uses, later refined to a single or a few proven benefits, buckthorn bark throughout its history has been consistently used to relieve one ailment: constipation and its by-products (hemorrhoids and anal irritation). Buckthorn bark contains compounds called anthraquinones, which have a strong purgative, laxative effect on the body. Because these compounds are powerful, before being processed into laxative products the bark is aged for a year, or heated and dried. Buckthorn bark has laxative and cathartic properties.