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Milk Thistle

What is milk thistle?

Milk thistle (Silybum marianum ), a common herb with spiny white-veined leaves and pink flowers, has been used as a liver tonic for at least 2,000 years. In this case, the ancients may have been on to something. Milk thistle seed extract contains a group of substances called silymarin that may help protect the liver. Some human studies suggest that milk thistle seed extract might be helpful for treating alcoholic liver disease, drug-induced liver disease, bile duct inflammation and chronic hepatitis.

One study of 170 patients with cirrhosis (chronic scarring of the liver, often caused by alcoholism) found that those who took milk thistle extract survived longer than those who took placebos (dummy pills). In another small study, it significantly improved symptoms of chronic hepatitis. However, more research is needed to verify these results. A review of previous studies published in 2005 concluded that there still wasn't enough evidence to say one way or another whether milk thistle is really helpful for people with alcohol-induced liver disease or hepatitis.

How does milk thistle work?

Silymarin is a mixture of chemical compounds (called flavonolignans) that may help protect and even repair the liver. Researchers hypothesize that it blocks toxins from entering liver cells. The liver is the only organ that can regenerate itself, and silymarin may accelerate this process by stimulating the production of the proteins that are the building blocks of new liver cells. Finally, some data suggests that silymarin is an antioxidant, which means it might protect cells from damage by scavenging oxygen molecules called free radicals.

How safe is milk thistle?

The vast majority of milk thistle users report no side effects, but a few have experienced a mild laxative effect. Although no interactions have been reported, laboratory research suggests that milk thistle has the potential to interact with many prescription drugs. If you take prescription medicines, check with your pharmacist or physician before using milk thistle. If you suspect you have a serious liver condition, see a doctor immediately for a diagnosis and appropriate treatment options.

What's the best way to take it?

Human studies have used milk thistle seed extract containing 70 percent silymarin. Keep in mind, though, that the government doesn't regulate herbal remedies as strictly as it does drugs, so quality and potency can vary from product to product. In rare cases supplements may be contaminated with undesirable substances. A typical dose for chronic liver conditions is one or two 200 milligram capsules a day. The herb is not effective as a tea. Also, don't confuse milk thistle with blessed thistle (Cnicus benedictus), which some people take to stimulate the appetite.


Mayo Clinic. Milk Thistle (Silybum marianum). 2010.

Rambaldi A. et al. Milk thistle for alcoholic and/or hepatitis B or C virus liver disease. Cochrane Review. 2005.

National Cancer Institute. Milk thistle. 2010.

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