Milk thistle (Silybum marianum) is a flowering herb utilized for its potentially protective effects on the liver. Although the mechanism of action is not fully understood, one explanation may be that it concentrates in the hepatocytes and competes with toxins for hepatocyte binding and penetration. Preliminary clinical evaluations of milk thistle for cirrhosis of the liver indicate potential benefits in healthier patients with alcoholic cirrhosis. However, major flaws in many of the studies make it difficult to draw solid conclusions. Milk thistle appears to be relatively safe, even with long-term use.