From Citizendium - Reading time: 1 min

Anthraquinone is the class-defining compound for a number of naturally-occurring plant pigments. Anthraquinone itself has been associated with causing liver, bladder and kidney cancers, and other non-neoplastic disorders.[1]. It also, however, has been a starting point for developing antineoplastic agents, especially the anthracycline agents, of which doxorubricin (Adriamycin) is best known. [2]
The plant Rheum palmatum, called Indian rhubarb in North America and also used in traditional Chinese medicine is rich in anthraquinones.
Anthraquinone derivatives called sennosides are used as cathartics; they are the active principle in senna extract.