Milk Thistle (PDQ®): Complementary and alternative medicine - Patient Information [NCI]

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Milk Thistle (PDQ®): Complementary and alternative medicine - Patient Information [NCI]

This information is produced and provided by the National Cancer Institute (NCI). The information in this topic may have changed since it was written. For the most current information, contact the National Cancer Institute via the Internet web site at or call 1-800-4-CANCER.

Milk Thistle


  • Milk thistle is a plant whose fruit and seeds are used to make remedies for liver and bile duct ailments (see Question 1).
  • The active ingredient found in milk thistle is silymarin, an antioxidant that, among other things, protects against cell damage and stimulates repair of liver tissue (see Question 1 and Question 5).
  • Milk thistle has been studied in laboratory cell lines and animal tumors for its potential to make chemotherapy less toxic and more effective, and to slow the growth of cancer cells (see Question 3 and Question 5).
  • Milk thistle is usually taken in capsules or tablets (see Question 4).
  • Milk thistle has been studied in a clinical trial of children with leukemia (see Question 6).
  • Very few bad side effects from the use of milk thistle or silymarin have been reported (see Question 7).
  • It is not known if milk thistle may make anticancer medications or other drugs more or less effective when taken with them (see Question 7).
  • The U.S. Food and Drug Administration has not approved the use of milk thistle as a treatment for cancer or any other medical condition (see Question 8).
  • Milk thistle is available in the United States as an herbal dietary supplement (see Question 8).

Questions and Answers About Milk Thistle

What is milk thistle?

Milk thistle is a plant whose fruit and seeds have been used for more than 2,000 years as a treatment for disorders of the liver, bile ducts, and gallbladder. Milk thistle is native to Europe but can also be found in the United States and South America.

The medicinal ingredient found in milk thistle is silymarin, an extract of milk thistle seeds. It is an antioxidant that protects against cell damage. Silymarin contains 4 compounds: silybin (the most active), isosilybin, silychristin, and silydianin. Most research has studied silymarin or its major compound silybin, instead of the plant in its whole form.

The botanical name for milk thistle is Silybum marianum. Milk thistle is also called holy thistle, Marian thistle, Mary thistle, St. Mary thistle, Our Lady's thistle, wild artichoke, Mariendistel (German), and Chardon-Marie (French).

What is the history of the discovery and use of milk thistle as a complementary and alternative treatment for cancer?

The ancient Greeks and Romans used milk thistle as a treatment for liver ailments and snake bites. During the Middle Ages, milk thistle was recommended to treat liver toxins. Modern homeopathic practitioners have used compounds from milk thistle seeds to treat a range of disorders including jaundice, gallstones, and peritonitis. The German Commission E, which studies the safety and efficacy of herbs for the German government, recommends milk thistle for liver damage due to toxins, cirrhosis of the liver, and as a supportive therapy for chronic inflammation of the liver.

Despite milk thistle's long history of use for liver complaints, it was not until 1968 that researchers extracted silymarin from milk thistle seeds and suggested that it might be the plant's active ingredient. Silymarin was later discovered to be a mixture of flavonolignans, a family of plant-based substances with antioxidant effects.

What is the theory behind the claim that milk thistle is useful in treating cancer?

To research the claim that milk thistle is useful in treating cancer, its active substance silymarin and its major compound silybin have been the most widely studied ingredients.

Silymarin and silybin may protect the liver against damage from toxic chemicals by blocking toxins from entering the cell or by moving toxins out of the cell before damage begins.

Silymarin and silybin have been studied in the laboratory in cancer cells as well as in animal tumors of the tongue, skin, bladder, colon, and small intestine. They have been tested for their potential to:

  • Make chemotherapy less toxic.
  • Make chemotherapy more effective.
  • Stop or slow the growth of cancer cells and block tumors from starting or continuing to grow.
  • Help to repair liver tissue.
How is milk thistle administered?

Milk thistle is usually taken by mouth in capsules or tablets. Since it does not dissolve well in water, it is not commonly taken as an herbal tea. In Europe, the active compound silybin is given by intravenous infusion as the only effective antidote for Amanita phalloides, a rare mushroom toxin that causes deadly liver failure.

Most milk thistle supplements are measured by how much silybin they contain. Special forms of silybin made to be easily absorbed and used by the body are sold under the names Legalon, silipide, and Siliphos.

Have any preclinical (laboratory or animal) studies been conducted using milk thistle?

Research in a laboratory or using animals is done to find out if a drug, procedure, or treatment is likely to be useful in humans. Preclinical studies are done before clinical trials (in humans) are begun.

Silymarin, the active substance found in milk thistle seeds, has been studied in laboratory research. These studies have shown that it acts as an antioxidant by:

  • Strengthening cell walls to prevent toxins from crossing into the cell.
  • Stimulating enzymes that make toxins less harmful to the body.
  • Blocking damaging substances called free radicals from attacking cells.

Silybin, the major compound found in silymarin, has been studied in laboratory experiments using cancer cell lines (cells adapted to grow in the laboratory). These studies show that silybin:

  • May help cisplatin and doxorubicin (chemotherapy drugs) work better against ovarian and breast cancer cells.
  • May have direct anticancer effects against prostate, breast, and cervical cancer cells.
  • May slow down cell growth, as shown in prostate cancer cell lines.

In laboratory tests using rat livers, silymarin and silybin have also been found to boost the regrowth of liver tissue.

Tests on colorectal cancer cells transplanted into mice found that silybin given twice a day decreased tumor growth.

Have any clinical trials (research studies with people) of milk thistle been conducted?

There is 1 case report describing the use of silymarin in a patient with promyelocytic leukemia who required breaks in chemotherapy due to abnormal liver enzyme levels. During 4 months of treatment with silymarin, the patient had normal liver enzyme levels and was able to undergo chemotherapy without breaks. A second case report describes a patient with hepatocellular carcinoma whose symptoms improved when he took 450 milligrams of silymarin per day, without anticancer therapy.

A randomized clinical trial in children with acute lymphoblastic leukemia found that silymarin decreased the harmful effects of chemotherapy on the liver without working against the cancer treatment. The children taking silymarin needed fewer chemotherapy dose reductions because of side effects than the children who did not take milk thistle.

A number of clinical trials have studied milk thistle or silymarin in the treatment of patients with hepatitis, cirrhosis, or disorders of the bile ducts. These trials have used a wide range of doses with mixed results. In a trial of biologic therapy for patients with chronic hepatitis, patients taking silymarin had fewer symptoms and a better quality of life compared to patients not taking silymarin. The beneficial effects of silymarin shown in some studies suggest it might play a role in preventing hepatitis and/or liver cancer, but no clinical trials have studied the use of silymarin for prevention.

Have any side effects or risks been reported from milk thistle?

Very few bad side effects from the use of milk thistle or silymarin have been reported when taken as recommended. Several large, carefully designed studies in patients with liver disorders have found that taking silymarin may rarely have a laxative effect or cause nausea, heartburn, or stomach upset. At high doses, mild allergic reactions have been seen (more than 1,500 milligrams a day).

Silymarin has been used in pregnant women who have a bile blockage in the liver, with no toxic effects to the patient or fetus. Silymarin have also been given to children intravenously for mushroom poisoning.

It is not known if milk thistle may make anticancer medications or other drugs more effective, less effective, or have no effect when taken with them.

Is milk thistle approved by the U.S. Food and Drug Administration (FDA) for use as a cancer treatment in the United States?

The U.S. Food and Drug Administration (FDA) has not approved the use of milk thistle as a treatment for cancer or any other medical condition.

Milk thistle is available in the United States as a dietary supplement. Because dietary supplements are regulated as foods, not as drugs, FDA approval is not required unless specific claims about disease prevention or treatment are made.

Given the limited research done with milk thistle in patients with cancer, using it as a cancer treatment cannot be recommended except in carefully designed clinical trials.

Current Clinical Trials

Check NCI's list of cancer clinical trials for cancer CAM clinical trials on milk thistle and silymarin that are actively enrolling patients.

General information about clinical trials is available from the NCI Web site.

Changes to This Summary (03 / 23 / 2012)

The PDQ cancer information summaries are reviewed regularly and updated as new information becomes available. This section describes the latest changes made to this summary as of the date above.

Editorial changes were made to this summary.

General CAM Information

Complementary and alternative medicine (CAM)—also referred to as integrative medicine—includes a broad range of healing philosophies, approaches, and therapies. A therapy is generally called complementary when it is used in addition to conventional treatments; it is often called alternative when it is used instead of conventional treatment. (Conventional treatments are those that are widely accepted and practiced by the mainstream medical community.) Depending on how they are used, some therapies can be considered either complementary or alternative. Complementary and alternative therapies are used in an effort to prevent illness, reduce stress, prevent or reduce side effects and symptoms, or control or cure disease.

Unlike conventional treatments for cancer, complementary and alternative therapies are often not covered by insurance companies. Patients should check with their insurance provider to find out about coverage for complementary and alternative therapies.

Cancer patients considering complementary and alternative therapies should discuss this decision with their doctor, nurse, or pharmacist as they would any therapeutic approach, because some complementary and alternative therapies may interfere with their standard treatment or may be harmful when used with conventional treatment.

Evaluation of CAM Approaches

It is important that the same rigorous scientific evaluation used to assess conventional approaches be used to evaluate CAM therapies. The National Cancer Institute (NCI) and the National Center for Complementary and Alternative Medicine (NCCAM) are sponsoring a number of clinical trials (research studies) at medical centers to evaluate CAM therapies for cancer.

Conventional approaches to cancer treatment have generally been studied for safety and effectiveness through a rigorous scientific process that includes clinical trials with large numbers of patients. Less is known about the safety and effectiveness of complementary and alternative methods. Few CAM therapies have undergone rigorous evaluation. A small number of CAM therapies originally considered to be purely alternative approaches are finding a place in cancer treatment—not as cures, but as complementary therapies that may help patients feel better and recover faster. One example is acupuncture. According to a panel of experts at a National Institutes of Health (NIH) Consensus Conference in November 1997, acupuncture has been found to be effective in the management of chemotherapy-associated nausea and vomiting and in controlling pain associated with surgery. In contrast, some approaches, such as the use of laetrile, have been studied and found ineffective or potentially harmful.

The NCI Best Case Series Program, which was started in 1991, is one way CAM approaches that are being used in practice are being investigated. The program is overseen by the NCI's Office of Cancer Complementary and Alternative Medicine (OCCAM). Health care professionals who offer alternative cancer therapies submit their patients' medical records and related materials to OCCAM. OCCAM conducts a critical review of the materials and develops follow-up research strategies for approaches deemed to warrant NCI-initiated research.

Questions to Ask Your Health Care Provider About CAM

When considering complementary and alternative therapies, patients should ask their health care provider the following questions:

  • What side effects can be expected?
  • What are the risks associated with this therapy?
  • Do the known benefits outweigh the risks?
  • What benefits can be expected from this therapy?
  • Will the therapy interfere with conventional treatment?
  • Is this therapy part of a clinical trial?
  • If so, who is sponsoring the trial?
  • Will the therapy be covered by health insurance?

To Learn More About CAM

National Center for Complementary and Alternative Medicine (NCCAM)

The National Center for Complementary and Alternative Medicine (NCCAM) at the National Institutes of Health (NIH) facilitates research and evaluation of complementary and alternative practices, and provides information about a variety of approaches to health professionals and the public.

NCCAM Clearinghouse
Post Office Box 7923 Gaithersburg, MD 20898–7923
Telephone: 1–888–644–6226 (toll free) 301–519–3153 (for International callers)
TTY (for deaf and hard of hearing callers): 1–866–464–3615
Fax: 1–866–464–3616
Web site:

CAM on PubMed

NCCAM and the NIH National Library of Medicine (NLM) jointly developed CAM on PubMed, a free and easy-to-use search tool for finding CAM-related journal citations. As a subset of the NLM's PubMed bibliographic database, CAM on PubMed features more than 230,000 references and abstracts for CAM-related articles from scientific journals. This database also provides links to the Web sites of over 1,800 journals, allowing users to view full-text articles. (A subscription or other fee may be required to access full-text articles.) CAM on PubMed is available through the NCCAM Web site. It can also be accessed through NLM PubMed bibliographic database by selecting the "Limits" tab and choosing "Complementary Medicine" as a subset.

Office of Cancer Complementary and Alternative Medicine

The NCI Office of Cancer Complementary and Alternative Medicine (OCCAM) coordinates the activities of the NCI in the area of complementary and alternative medicine (CAM). OCCAM supports CAM cancer research and provides information about cancer-related CAM to health providers and the general public via the NCI Web site.

National Cancer Institute (NCI) Cancer Information Service

U.S. residents may call the NCI Cancer Information Service toll free at 1-800-4-CANCER (1-800-422-6237) Monday through Friday from 8:00 am to 8:00 pm. A trained Cancer Information Specialist is available to answer your questions.

Food and Drug Administration

The Food and Drug Administration (FDA) regulates drugs and medical devices to ensure that they are safe and effective.

Food and Drug Administration
5600 Fishers Lane
Rockville, MD 20857
Telephone: 1–888–463–6332 (toll free)
Web site:

Federal Trade Commission

The Federal Trade Commission (FTC) enforces consumer protection laws. Publications available from the FTC include:

  • Who Cares: Sources of Information About Health Care Products and Services
  • Fraudulent Health Claims: Don't Be Fooled
Consumer Response Center
Federal Trade Commission
Washington, DC 20580
Telephone: 1-877-FTC-HELP (1-877-382-4357) (toll free)
TTY (for deaf and hearing impaired callers): 202-326-2502
Web site:

About PDQ

PDQ is a comprehensive cancer database available on NCI's Web site.

PDQ is the National Cancer Institute's (NCI's) comprehensive cancer information database. Most of the information contained in PDQ is available online at NCI's Web site. PDQ is provided as a service of the NCI. The NCI is part of the National Institutes of Health, the federal government's focal point for biomedical research.

PDQ contains cancer information summaries.

The PDQ database contains summaries of the latest published information on cancer prevention, detection, genetics, treatment, supportive care, and complementary and alternative medicine. Most summaries are available in two versions. The health professional versions provide detailed information written in technical language. The patient versions are written in easy-to-understand, nontechnical language. Both versions provide current and accurate cancer information.

The PDQ cancer information summaries are developed by cancer experts and reviewed regularly.

Editorial Boards made up of experts in oncology and related specialties are responsible for writing and maintaining the cancer information summaries. The summaries are reviewed regularly and changes are made as new information becomes available. The date on each summary ("Date Last Modified") indicates the time of the most recent change.

PDQ also contains information on clinical trials.

A clinical trial is a study to answer a scientific question, such as whether one treatment is better than another. Trials are based on past studies and what has been learned in the laboratory. Each trial answers certain scientific questions in order to find new and better ways to help cancer patients. During treatment clinical trials, information is collected about the effects of a new treatment and how well it works. If a clinical trial shows that a new treatment is better than one currently being used, the new treatment may become "standard." Patients may want to think about taking part in a clinical trial. Some clinical trials are open only to patients who have not started treatment.

Listings of clinical trials are included in PDQ and are available online at NCI's Web site. Descriptions of the trials are available in health professional and patient versions. Many cancer doctors who take part in clinical trials are also listed in PDQ. For more information, call the Cancer Information Service 1-800-4-CANCER (1-800-422-6237).

Last Revised: 2012-03-23

If you want to know more about cancer and how it is treated, or if you wish to know about clinical trials for your type of cancer, you can call the NCI's Cancer Information Service at 1-800-422-6237, toll free. A trained information specialist can talk with you and answer your questions.

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