At some point before the 1500s, Native American tribes on the upper West Coast discovered the bowel cleansing properties of cascara sagrada and began to include it in their large chest of natural medicines. When Europeans arrived in the region, they quickly noticed the plants benefits and began to harvest and send the natural medicine back home. Four centuries later cascara accounted for 20 of sales in the category of stimulant laxatives in the U.S. The bark of cascara trees, like several other commercial plants in the category, contains anthraquinones, terpene compounds which may be responsible for its effects on the intestinal tract, especially the colon. Aloe vera, Senna and rhubarb root also demonstrate these properties. Anthraquinones may cause a reduction of the flow of electrolytes and water through the wall of the colon. This may cause the bowel contents to swell, which in turn, may stimulate colonic muscle contractions known as peristalsis. The result may be the gentle emptying of the bowel.