Cascara sagrada (Rhamnus purshiana) is a shrub native to western North America whose bark is processed for medicinal purposes. Cascara sagrada contains compounds called anthraquinones that have powerful laxative effects. Cascara sagrada is primarily used to treat constipation. The anthraquinones contained in the bark inhibit the absorption of water and electrolytes in the intestines. Because of this, stool volume increases as it absorbs the excess water, which increases pressure within the intestine. This stimulates muscle contractions in the colon (peristalsis), speeding the clearance of the bowel.*