Milk thistle protects the liver, stimulates secretion of bile, increases breast milk in nursing mothers, antidepressant. Silymarin, a substance contained in the seeds, maintains the liver's function and prevents damage from compounds that re normally highly toxic. This substance has been used successfully to treat hepatitis and cirrhosis of the liver. Protects the liver's many metabolic activities and helps renew its cells. Also used in the treatment of jaundice. Milk thistle can help limit the damage done to the liver by chemotherapy and speeds up the recovery from side effects once treatment is completed.

Milk thistle is featured in Hildegard of Bingen's Physica, the first herbal by a woman, written about 1150 and published in 1533, and other early European herbals mention its use for liver disease. The sixteenth-century English herbalist John Gerard considered it "the best remedy that grows against all liver diseases, and the eighteenth-century German physician Rademacher used the seed for chronic and acute liver diseases.

More than 300 studies conducted since the late 1960s provide an experimental basis for the effectiveness and safety of silymarin, the main chemical complex of milk thistle seeds, in the treatment of liver disease. Standardized seed preparations have been shown to alter the cell structure of the outer liver membrane which prevents toxic chemicals from entering and stimulates the liver's own capacity to generate new cells. Silymarin also scavenges harmful oxygen radicals in the liver, further protecting it.

German health authorities allow milk thistle preparations to be used in supportive treatment of chronic inflammatory liver disorders such as hepatitis, cirrhosis, and fatty infiltration caused by alcohol or other toxins. In addition to its well-documented curative action, silymarin can help prevent liver damage if it is taken before exposure to toxins.