Although milk thistle originally grew wild throughout much of Europe, it is now naturalized to the east coast of North America, California, and South America. This biennial grows up to 1 meter or 40 inches in height with spiny leaves that are marked with white along the veins. The plant is crowned with a bright pink-to-red flower head that produces numerous small seeds. Milk thistle has been used medicinally for several thousand years. Both the Greeks and the Romans noted its hepato-protective effects, however, current interest in this product did not begin until the late 1960s when silymarin, a combination of flavonolignans believed to be responsible for the hepatic activity, was first isolated from the ripe seeds.