Rhamnus purshiana (cascara buckthorn, cascara, bearberry, and in the Chinook Jargon, chittem and chitticum; syn. Frangula purshiana, Rhamnus purshianus) is a species of buckthorn native to western North America from southern British Columbia south to central California, and eastward to northwestern Montana.
The dried bark of cascara has been used for centuries as an herbal laxative – first by Native Americans in the Pacific Northwest, and then later by European/U.S. colonizers. The chemicals primarily responsible for the laxative action are the hydroxyanthracene glycosides (particularly cascarosides A, B, C and D), and emodin. These act as stimulant laxatives, with the hydroanthracene glycosides stimulating peristalsis, and emodin exciting smooth muscle cells in the large intestine.