Capsules: Variation in Milk Thistle Products

Newsbreaks in herb research: Milk thistle protects the liver but study shows that products may vary.

| November/December 1997

  • Milk thistle
    Photograph by Steven Foster

Commercial extracts of milk thistle provide effective liver protection, but they vary widely in the amount of active ingredients they contain, according to a recent study by researchers in New Mexico.

Animal and human studies have shown that milk thistle can protect the liver from damage by alcohol and other toxins. More than 300 studies con­ducted since the late 1960s show that silymarin, milk thistle’s active ingre­dient, can prevent toxins from entering the liver and increase the liver’s ability to generate new cells.

Most of the studies used a purified form of silymarin, and the New Mexico study shows that commercial extracts of milk thistle (Silybum marianum) provide liver protection similar to this purified silymarin.

However, although the commercial extracts protected laboratory animals from liver damage, the two bottles analyzed by the researchers contained varying amounts of silymarin (2.7 mg/ml and 4.1 mg/ml).

According to the researchers, the different silymarin content indicates that consumers can’t be sure of the amount of silymarin they’re taking. Also, more research is needed to determine the precise effective dose.


Wang, M., et al. “Hepatoprotective properties of Silybum marianum herbal preparation on ethanol-induced liver damage.” Fitoterapia 1996, 67(2):166-171.

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