Milk thistle seed (Silybum marianum) has a history dating back over two thousand years as a favorite among herbalists for its positive effects on the liver and gallbladder. The seeds contain the highest concentrations of the active compound, silymarin. Silymarin is an antioxidant that reduces free radical production and oxidative damage. It may also inhibit the binding of toxins to the liver. In animals, silymarin reduces liver injury caused by acetaminophen and has been shown to have positive effects on alcoholic liver disease, hepatitis, and toxin-induced liver concerns.