Healers have used the prickly milk thistle plant to treat liver ailments for more than 2, 000 years. Somehow these early practitioners figured out that preparations of this purple-flowered member of the sunflower family could stimulate the flow of bile from the liver, improving digestion and various liver-related ills.

Interestingly, bile and other bodily fluids, also known as humors, were once associated with different personality types. Because it was thought that black bile was inherent to a melancholic nature, milk thistle was prescribed for treating depression and melancholy (which actually means "black bile"). Today, the word "biliousness" and the phrase "having excess bile" are still used to describe negative personality traits.