Milk thistle is a flowering herb that is native to the Mediterranean region. The seeds contain an antioxidant flavonoid complex known as silymarin, used traditionally to promote healthy liver function. Silymarin may inhibit the depletion of glutathione, an amino acid that plays a part in the body's overall defense system, as well as the liver's ability to detoxify. As an antioxidant, silymarin may have free-radical scavenging properties, allowing it to absorb harmful reactive atoms than can damage other molecules. It supports the liver's ability to function properly and may help the liver with synthesis of new proteins.