Herbal Preparations: Milk Thistle

Milk Thistle

Milk thistle (Silybum [Carduus] marianus) is a spiny European plant with white-veined leaves and milky sap, the seed of which is used to treat liver disease. Milk this-tle seed extract is used orally in the treatment of alco-holic and other cirrhoses and in Europe intravenously for its hepatoprotective effect in Amanita and other mushroom poisonings. It is grown in this country pri-marily as a “liver cleanser” and is reputed to protect this organ from a wide array of toxins. Milk thistle seed con-tains the active principle silymarin, a complex of flavonolignan compounds including silibinin (silybin), silidianin, and silychristin.

Mechanism of Action

Silymarin is thought to protect the liver by preventing the entry of toxins into the hepatocyte and by stimulat-ing nucleolar polymerase A, which, in turn, increases protein synthesis and liver regeneration. Silymarin un-dergoes enterohepatic circulation, increasing its con-centration in hepatocytes. It is also an antioxidant in its own right and is considered to have some cytoprotec-tive effect against carcinogens.

Indications

Alcoholic cirrhosis has been improved (faster return of liver enzymes to baseline) in at least three trials, al-though one multicenter Spanish study failed to demonstrate any change in the clinical course. There is no evidence to support the use of milk thistle to in-crease alcohol tolerance, although it is certainly being used for this purpose. The effectiveness of silymarin for viral hepatitis is not clear, although several trials demonstrated enough benefit to encourage further studies.

Intravenous silymarin has been demonstrated to lower mortality from Amanita mushroom poisonings, but this formulation is available only in Europe. Animal studies have demonstrated hepatic protection against alcohol, acetaminophen, and mushroom toxins and pro-tection against hepatic fibrosis with bile duct occlusion. There is also evidence of silybin protecting against cis-platin-induced nephrotoxicity in rats. It is not yet clear whether milk thistle extract offers any renal protection to humans.

Adverse Reactions, Contraindications, and Interactions

Milk thistle appears to be remarkably safe, with loose stools due to increased bile solubility and occasional al-lergic reactions being the common side effects. It has not been evaluated in children or in pregnant women. There are no known serious drug or herb interactions.

Dosage

Dry extract capsules standardized to 70% silymarin (calculated as silibinin) are administered at 200 to 400 mg/day or 12 to 15 g of dried seed per day. Teas are not recommended, since silymarin is not water soluble.

Conclusion

Milk thistle has shown promise in improving liver func-tion parameters in various hepatotoxic situations, such as alcoholic cirrhosis and mushroom poisoning. It is still unclear whether it will offer protection against viral hepatitis and various nephrotoxic agents.