A substance derived from any of several Old World coarse prickly-leaved shrubs and subshrubs including the plant Silybum marianum. Milk thistle's active chemical component is silymarin, which is a combination of flavonoids such as silibinin, dehydrosilibinin, silychristin and silydianin. These compounds are antioxidants and may alter the membrane structure of the liver cell, thereby blocking the absorption of toxins; they may also stimulate the production of new liver cells. In addition, milk thistle may increase cellular adenosine triphosphate (ATP) levels, exhibiting dose-dependent cardiac myocyte cytoprotection against doxorubicin. The silibinin component of milk thistle has been shown to inhibit growth factor receptor-mediated mitogenic and cell survival signaling, thereby inhibiting tumor growth. (NCI04) or A plant that has been used in some cultures to treat certain medical problems, including stomach, liver, and gallbladder disorders. The active extract of milk thistle seeds is called silymarin. It is being studied in the prevention of liver damage caused by some cancer treatments. Also called Silybum marianum.