Milk Thistle – What Does the Scientific Evidence Say?

Milk ThistleMilk thistle is one of the most popular herbal products sold in the United States, with retail sales around $9 million in 2000, and its sales continues to rise. It has been used medicinally for over 2 millenia, in particular for the treatment of hepatic and biliary disorders, but what does the scientific evidence say for its common use?

A flavonoid complex called silymarin is believed to be its active component. Silibinin is the most active component of silymarin and can inhibit the 5-lipoxygenase pathway that is involved in the formation of free radicals, scavenge hydroxyl radicals, and inhibit tumor necrosis factor (TNF). Animal models support the concept of milk thistle playing a role as an antioxidant that reduces free radical generation and affects cell growth, and thus can reduce inflammation and support the liver’s tolerance of oxidative stress, including damage induced by toxins such as carbon tetrachloride. However, what do human studies say?

Four systematic reviews of the literature have been reported. One review showed no improvements in liver function both by histology and biochemical testing. In the other reviews, milk thistle did not influence the course of alcoholic or hepatitis B or C disease by outcomes of mortality and histology, but it may have the potential to affect liver injury, demonstrated by improvements seen in liver function tests after acute injury.

The National Institutes of Health’s National Center for Complementary and Alternative Medicine (NCCAM) emphasizes the lack of definitive evidence for milk thistle’s efficacy in treating hepatitis C and recommends that patients not replace conventional medical therapy with milk thistle. However, since milk thistle has a long track record of uncommon adverse effects, with mild gastrointestinal disturbance in the form of a laxative as the most common, the German Commission E has approved milk thistle for use in liver conditions, including toxin-induced damage and liver cirrhosis in addition to dyspepsia.

A recent review of an integrative medicine strategy for alcohol abuse advocates a best-scientific evidence, balanced holistic approach, including nutritional counseling, healthy lifestyle changes, relaxation, judicious use of supplementation with B vitamins, probiotics, zinc, carnitine, and botanical products such as milk thistle, acupuncture, and mind-body therapy.

Milk thistle is commonly used in gastroenterology clinics to treat hepatitis and liver cirrhosis and in oncology as a hepatoprotectant to clear toxins, assuage symptoms of cancer, and improve tolerance to chemotherapy. Preliminary studies suggest that milk thistle may be beneficial in treating or preventing some cancers, such as skin, prostate, tongue squamous cell cancer, bladder, breast, cervical, colon, and leukemia.

A recent dermatologic review examined the use of topical milk thistle as a protectant against ultraviolet (UV) radiation and concluded that it falls under the category of a botanical cosmecuetical with antioxidant properties that may offset the effects of skin aging and skin cancer. Just preliminary conclusion based primarily on animal studies and awaiting human studies to validate anti-skin aging and skin cancer properties of milk thistle, which in the meanwhile is out on the market as silymarin found in moisturizers for photoaging, such as RosaCure+ and SkinCeuticals Antioxidant Lip Repair.

Tobey Leung, M.D.

Tobey Leung Physician and Grandmaster Martial Artist

Dr. Leung sub-specializes in sports medicine, occupational health, and interventional pain management. He developed an integrated theory in the behavioral sciences during the year 2000.

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