Chinese rhubarb comes from the dried root of Rheum palmatum or Rheum officinale. Compounds called anthraquinones (emodin, rhein, and others) pull more water into the bowel and trigger stronger contractions. This produces a strong laxative effect. People usually take a powder, extract, or capsule in the evening so they can pass a bowel movement the next morning.
Start with a small amount. Use it only for a few days at a time. Long or heavy use often causes cramping, diarrhea, and lost electrolytes.
Avoid Chinese rhubarb during pregnancy, while nursing, or if you have an intestinal blockage, inflammatory bowel disease, or kidney trouble. It can clash with water pills, heart drugs, and other laxatives.