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. Silymarin is a mixture that contains several closely related compounds, including silybin (consisting of the silybins A and B), isosilybin (consisting of the isosilybins A and B), silychristin and isosilychristin, silydianin, and taxifolin. Most research has studied silymarin or its major component 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 therapy?
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.
What is the theory behind the claim that milk thistle is useful in treating cancer?
The active substance in milk thistle is silymarin, containing silybin as its major compound. To research the claim that milk thistle is useful in treating cancer, silymarin and 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.
Can milk thistle make anticancer medications or other drugs more effective?
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. Specifically, it has not yet been determined whether milk thistle will increase or decrease how well chemotherapy works, or have no effect on it.
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 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:
- Strengthens cell walls to prevent toxins from crossing into the cell.
- Stimulates enzymes that make toxins less harmful to the body.
- Blocks damaging substances called free radicals from attacking cells.
Silybin A and B, the major components of silymarin, have been studied in laboratory experiments using cancer cell lines (cells adapted to grow in the laboratory). These studies suggest that these silybins:
- 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, and may also prevent the development of cancer.
- 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.
In laboratory tests using rats and mice whose ovaries have been removed, milk thistle has been found to help stop bone loss.
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?
Several small studies have looked at the effects of milk thistle on decreasing harmful effects of cancer treatment and whether milk thistle can be used to treat cancer.
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 randomized clinical trial in men who had surgery to remove their prostate found that a combination of silymarin and selenium improved quality of life, decreased cholesterol, and increased the amount of selenium in the blood.
A nonrandomized observational study in women with breast cancer who had surgery and radiation therapy found that a silymarin-based cream helped prevent patients from having skin reactions to radiation therapy.
A phase I clinical trial in 3 patients with advanced liver cancer and poor liver function aimed to find out the maximum dose of silybin phosphatidylcholine that patients can safely handle. One patient showed some improvement in liver function and signs of inflammation.
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.
Silymarin has been found to increase the effectiveness of iron chelation therapy, which removes extra iron in the blood of patients who have had many blood transfusions.
Have any side effects or risks been reported from milk thistle?
Very few 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.
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. Dietary supplements are products meant to be added to the diet. They are not drugs and are not meant to treat, prevent, or cure diseases. The manufacturer is responsible for ensuring that the product is safe and that the label claims are truthful and not misleading. The FDA does not approve dietary supplements as safe or effective before they are sold.
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.