This complementary and alternative medicine (CAM) information summary provides an overview of the use of milk thistle as a treatment and adjunct agent in cancer therapy.

The summary includes a brief history of milk thistle, a review of the laboratory studies and clinical trials, and a description of adverse effects associated with milk thistle use.

This summary contains the following key information:

• Milk thistle is a plant whose fruit and seeds have been used for more than 2,000 years as a treatment for liver and biliary disorders.



• The active substance in milk thistle, silymarin, is a mixture of flavonolignans, primarily consisting of four isomers: silybin, isosilybin, silychristin (also known as silichristin), and silydianin (also known as silidianin). In the biological literature, silybin is referred to as silibinin.



• Laboratory studies demonstrate that silymarin functions as a potent antioxidant, stabilizes cellular membranes, stimulates detoxification pathways, stimulates regeneration of liver tissue, inhibits the growth of certain cancer cell lines, exerts direct cytotoxic activity toward certain cancer cell lines, and may increase the efficacy of certain chemotherapy agents.



• Human clinical trials have investigated milk thistle or silymarin primarily in individuals with hepatitis or cirrhosis. No clinical trials in individuals with cancer have been published.



• Few adverse side effects have been reported for milk thistle, but little information about interactions with anticancer medications or other drugs is available.



• Milk thistle is available in the United States as a dietary supplement.

Many of the medical and scientific terms used in the summary are hypertext linked (at first use in each section) to the NCI Dictionary ¹, which is oriented toward nonexperts. When a linked term is clicked, a definition will appear in a separate window. All linked terms and their corresponding definitions will appear in a glossary in the printable version of the summary.

Reference citations in some PDQ CAM information summaries may include links to external Web sites that are operated by individuals or organizations for the purpose of marketing or advocating the use of specific treatments or products. These reference citations are included for informational purposes only. Their inclusion should not be viewed as an endorsement of the content of the Web sites, or of any treatment or product, by the PDQ Cancer CAM Editorial Board or the National Cancer Institute (NCI).

Glossary Terms

In cancer therapy, a drug or substance used in addition to the primary therapy.

An unwanted side effect of treatment.

A substance that protects cells from the damage caused by free radicals (unstable molecules made by the process of oxidation during normal metabolism). Free radicals may play a part in cancer, heart disease, stroke, and other diseases of aging. Antioxidants include beta-carotene, lycopene, vitamins A, C, and E, and other natural and manufactured substances.

Having to do with the liver, bile ducts, and/or gallbladder.

The individual unit that makes up the tissues of the body. All living things are made up of one or more cells.

A drug used to treat cancer.

A type of chronic, progressive liver disease in which liver cells are replaced by scar tissue.

A type of research study that tests how well new medical approaches work in people. These studies test new methods of screening, prevention, diagnosis, or treatment of a disease. Also called clinical study.

Forms of treatment that are used in addition to (complementary) or instead of (alternative) standard treatments. These practices generally are not considered standard medical approaches. Standard treatments go through a long and careful research process to prove they are safe and effective, but less is known about most types of CAM. CAM may include dietary supplements, megadose vitamins, herbal preparations, special teas, acupuncture, massage therapy, magnet therapy, spiritual healing, and meditation. Also called CAM.

Cells of a single type (human, animal, or plant) that have been adapted to grow continuously in the laboratory and are used in research.

Cell-killing.

A product that is added to the diet. A dietary supplement is taken by mouth, and usually contains one or more dietary ingredient (such as vitamin, mineral, herb, amino acid, and enzyme). Also called nutritional supplement.

Effectiveness. In medicine, the ability of an intervention (for example, a drug or surgery) to produce the desired beneficial effect.

Disease of the liver causing inflammation. Symptoms include an enlarged liver, fever, nausea, vomiting, abdominal pain, and dark urine.

One of two or more compounds that have the same chemical formula but different arrangements of the atoms within the molecules and that may have different physical/chemical properties.

Research done in a laboratory. These studies may use test tubes or animals to find out if a drug, procedure, or treatment is likely to be useful. Laboratory studies take place before any testing is done in humans.

A large organ located in the upper abdomen. The liver cleanses the blood and aids in digestion by secreting bile.

A very thin layer of tissue that covers a surface.

A plant that has been used in some cultures to treat certain medical problems, including stomach, liver, and gallbladder disorders. The active extract of milk thistle seeds is called silymarin. It is being studied in the prevention of liver damage caused by some cancer treatments. Also called Silybum marianum.

A problem that occurs when treatment affects healthy tissues or organs. Some common side effects of cancer treatment are fatigue, pain, nausea, vomiting, decreased blood cell counts, hair loss, and mouth sores.

A substance obtained from milk thistle seeds that is being studied in the prevention of liver damage caused by certain cancer treatments.