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Milk Thistle

Other common name(s): Mary thistle, Marian thistle, holy thistle, lady thistle, silymarin

Scientific/medical name(s): Silybum marianum


Milk thistle, a plant belonging to the same family as daisies, is native to the Mediterranean regions and grows in Europe, North America, South America, and Australia. The ripe seeds are used to make herbal remedies. They contain the antioxidant silymarin, which is thought to be responsible for milk thistle's helpful effects. Silymarin is a combination of 3 different compounds: silybinin (also called silybin or silibinin), silidyanin (also spelled silidianin), and silychristin (also spelled silichristin).


A few studies have suggested that silymarin, an antioxidant, may be useful for treating certain types of liver diseases in humans such as cirrhosis or chronic hepatitis. Most of the studies did not show improved survival, although laboratory tests showed an improvement in liver function in some. One small study found that it seemed to help protect liver function in children getting chemotherapy for cancer. Larger randomized clinical trials are needed to determine whether these effects are reliable. Early studies in test tubes and laboratory animals have suggested that silymarin may help with cancer prevention and treatment. Human studies are needed to find out what role silymarin may play in preventing or treating cancer in people.

How is it promoted for use?

Proponents claim that milk thistle detoxifies and protects the liver and is an effective treatment for hepatitis C, jaundice, and cirrhosis. They also claim it strengthens the spleen and gallbladder, benefits people with diabetes, and slows the growth of certain types of cancer, including skin cancer, breast cancer, and prostate cancer. Some believe that milk thistle is an antidote for certain varieties of poisonous mushrooms.

Proponents also state that silymarin is a potent antioxidant. Antioxidants are compounds that block the action of activated oxygen molecules called free radicals, which can damage cells.

What does it involve?

Milk thistle supplements are made from the ripe seed, which is actually the fruit of the plant. The supplement is available as a capsule, tablet, powder, and liquid extract. Powdered milk thistle can be made into a tea. A typical daily dose ranges from 140 to 400 milligrams of silymarin, usually divided into 2 or 3 doses. The leaves, flower, roots, and stalk of the milk thistle plant contain very little silymarin and are usually not used in supplements.

What is the history behind it?

Milk thistle has been used for thousands of years in Europe as a liver restorative. It was recommended to treat malaria, melancholy, plague, and many other illnesses. It was also thought to reduce the effects of toxins such as poisonous mushrooms and alcohol on the liver. All parts of the milk thistle plant have been eaten as food in European countries, and its seeds have been made into a drink similar to coffee. Only recently have scientists begun to test its effectiveness in treating illness.

What is the evidence?

Silymarin has been studied extensively in the laboratory for the treatment of short-term and chronic liver diseases, and to a lesser extent for some types of cancer. Some research indicates that silymarin may be useful for treating certain liver diseases, particularly those caused by exposure to toxins. Commission E (Germany's regulatory agency for herbs) approved the use of milk thistle fruit (the part of the plant that contains silymarin) as a treatment for toxic liver disease and a supportive treatment for chronic inflammatory liver disease and cirrhosis of the liver.

One review of both clinical and laboratory research found that silymarin may be effective for patients with hepatitis, alcoholic liver disease, and cirrhosis. However, the researchers noted that all of the clinical trials were conducted outside of the United States, were difficult to interpret, involved small numbers of patients, and were not consistent in following scientific methods.

More recently, a group reviewed studies of the use of milk thistle for alcoholic or viral hepatitis and observed problems with study methods in most of them. For example, fewer than half of the studies were properly double-blinded, meaning participants or researchers might have been aware of which substance was being tested. In the clinical trials that were properly conducted, milk thistle did not show any effect.

A small pilot study published in 2009 looked at milk thistle in children to find out if it helped protect the liver from the chemotherapy drugs they were getting for leukemia. The children who got milk thistle had somewhat better liver function afterward, as measured by lab tests. More research is needed to find out if this holds true in future studies and for other kinds of chemotherapy drugs.

Studies in laboratory mice have concluded that silymarin provided some protection against skin cancer caused by chemical carcinogens or ultraviolet radiation, possibly because of its antioxidant properties. Studies using cancer cells grown in a laboratory and mouse studies found that silymarin reduced growth of breast, prostate, and cervical cancer cells. These test tube studies also suggested that silymarin may be able to enhance the effectiveness of some chemotherapy drugs. Further studies are required to find out whether the results apply to humans. Preliminary clinical studies in cancer patients indicate that silymarin does not cause serious side effects. However, studies of anti-cancer activity in human patients have not been published as of 2008.

A study of rats given a type of chemotherapy that often harms the kidneys showed less kidney damage in rats that were also given silymarin. Again, human studies are needed to learn whether this effect might also happen in people.

Are there any possible problems or complications?

This product is sold as a dietary supplement in the United States. Unlike companies that produce drugs (which must provide the FDA with results of detailed testing showing their product is safe and effective before the drug is approved for sale), the companies that make supplements do not have to show evidence of safety or health benefits to the FDA before selling their products. Supplement products without any reliable scientific evidence of health benefits may still be sold as long as the companies selling them do not claim the supplements can prevent, treat, or cure any specific disease. Some such products may not contain the amount of the herb or substance that is written on the label, and some may include other substances (contaminants). Though the FDA has written new rules to improve the quality of manufacturing processes for dietary supplements and the accurate listing of supplement ingredients, these rules do not take full effect until 2010. And, the new rules do not address the safety of supplement ingredients or their effects on health when proper manufacturing techniques are used.
Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

Silymarin is generally considered safe. A few people have reported stomach upset such as nausea, abdominal pain, diarrhea, and vomiting, although this is thought to have been due to contamination of the supplement with outside substances, not the silymarin itself. Large doses of silymarin may have a laxative effect. Allergic reactions are rare, but may be more common among people who are allergic to plants in the same family, such as ragweed, chrysanthemums, marigolds, and daisies. Anyone who has hives, shortness of breath, dizziness, or swelling in the mouth or throat after taking silymarin should call emergency services right away. Studies have not been done to test silymarin’s safety in children or in pregnant or breast-feeding women.

In general, antioxidant supplements are not recommended during chemotherapy or radiation therapy for cancer, since they can block some of the cancer-killing effects of these treatments.

In addition, the potential interactions between silymarin and other drugs and herbs should be considered. Some of these combinations may be dangerous. Always tell your doctor and pharmacist about any herbs you are taking. Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

Additional resources

More information from your American Cancer Society

The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-ACS-2345).

Dietary Supplements: What Is Safe?

The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management

Complementary and Alternative Methods and Cancer

Placebo Effect

Learning About New Ways to Treat Cancer

Learning About New Ways to Prevent Cancer


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Zi X, Grasso AW, Kung HJ, Agarwal R. A flavonoid antioxidant, silymarin, inhibits activation of erbB1 signaling and induces cyclin-dependent kinase inhibitors, G1 arrest, and anticarciniogenic effects in human prostate carcinoma DU145 cells. Cancer Res. 1999;59:622-632.

Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.

Last Medical Review: 11/28/2008
Last Revised: 12/15/2009