Pharmacology. Extracts of the milk thistle plant have been used since ancient times to treat a variety of hepatic and biliary disorders, including cholestasis, jaundice, cirrhosis, acute and chronic hepatitis, and primary malignancies, and to protect the liver against toxin-induced injury. The extract of the ripe seeds and leaves contains 70–80% silymarin, a flavanolignan mixture of which silibinin is the most biologically active constituent. The hypothesized mechanism of action is twofold: alteration of hepatocyte cell membrane permeability, preventing toxin penetration; and increased ribosomal protein synthesis, promoting hepatocyte regeneration.
Although the efficacy of silibinin has not been established in controlled studies in humans, it has been associated with reduced liver damage when administered intravenously in the treatment of amatoxin mushroom poisoning. Competitive inhibition of amatoxin entry via the membrane transport system for bile salts has been demonstrated. Silibinin also appears to inhibit tumor necrosis factor (TNF) release in the injured liver, thus slowing the process of amatoxin-induced apoptosis. There is recent evidence that a continuous infusion of silibinin can effectively suppress viral load in patients with hepatitis C.
Silymarin also is reported to have antifibrotic, anti-inflammatory, and antioxidant activity and may have therapeutic efficacy in the treatment of prostate and skin cancer. There is preliminary evidence that milk thistle constituents may also protect against the nephrotoxic effects of drugs such as acetaminophen, cisplatin, and vincristine.