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Milk Thistle

(Silymarin)

By Melissa G. Marko, PhD, Ara DerMarderosian, PhD

Milk thistle ( Silybum marianum) is a purple-flowered plant. Its sap and seeds contain the active ingredient silymarin, a potent antioxidant and a term often used interchangeably with milk thistle. Silymarin can be further divided into 3 primary flavonoids: silybin, silydianin, and silychristin. Extracts of milk thistle should be standardized to 80 percent silymarin.

Claims

Milk thistle is said to treat cirrhosis and to protect the liver from viral hepatitis, the damaging effects of alcohol, and hepatotoxic drugs (1). Milk thistle may also improve glycemic control in type 2 diabetes (2) and individual case reports claim fatality reduction in mushroom poisoning (3).

Evidence

A 2007 Cochrane review of 13 randomized clinical trials assessed milk thistle in 915 patients with alcoholic and/or hepatitis B or C virus liver diseases (4). Data from this analysis determined that intervention had no significant effect on all-cause mortality, complications of liver disease, or liver histology. When all trials were included in the analysis, liver-related mortality was significantly reduced; however, in an analysis limited to high-quality studies, this reduction was not significant. Milk thistle was not associated with a significant increase in adverse effects. The design of these clinical trials did come into question, and the authors questioned the benefits of milk thistle and suggested the need for more well-designed placebo-controlled studies. In vitro, silymarin increases levels of intrahepatic glutathione, an antioxidant important for detoxification (5).

Another recent analysis of 9 randomized, placebo-controlled trials (487 patients) (2) indicates that milk thistle may improve glycemic control in type 2 diabetes; however, the studies were small and therefore further high-quality, large controlled trials using standardized preparation are needed before beneficial claims are justified.

Recently, 2 cases of Amanita mushroom ingestion poisoning (3) showed favorable results after treatment with silybin.

Adverse effects

No serious adverse effects have been reported. Women who have hormone-sensitive conditions (eg, breast, uterine, and ovarian cancer; endometriosis; uterine fibroids) should avoid the above-ground parts of milk thistle.

Drug interactions

Milk thistle may intensify the effects of antihyperglycemic drugs (6) and may interfere with indinavir therapy (7). Silybin inhibits phase 1 and 2 enzymes and inactivates cytochromes P450 3A4 and 2C9.

Milk thistle references

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