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Milk Thistle

Milk thistle, also referred to as St. Mary’s thistle, lady thistle, or holy thistle, originated in the Mediterranean region and was grown and used as a vegetable throughout Europe. It was brought to the United States and has adapted to life in the wild in California and along the East Coast.

It is a tall plant with large prickly leaves and a reddish purple flower. The sap is white and milky, perhaps explaining at least one of its common names.

The white spots along the ribs of the leaves were said to have been drops of the Virgin Mary’s milk. The herb was used in times past to help encourage milk production, but this may have been due to the name and the association.

The medicinal use of milk thistle goes back two thousand years. Pliny the Elder wrote of it, praising its value for “carrying off bile.”

Medieval herbalists also made use of this property, and in the sixteenth century English herbalists adopted it. It did not maintain its popularity, however, and by the early twentieth century only homeopaths were familiar with it.

With a renewal of interest in herbal medicines, researchers started to investigate milk thistle scientifically in the 1950s.

The part of the plant that is used is the small hard fruit with the fuzz (technically called “pappus”) removed.

Active Ingredients

Silymarin, which makes up from 1 to 4 percent of milk thistle fruits, is itself actually a combination of chemicals called flavonolignans.

In addition to these, the seeds contain fatty acids and flavonoids, including apigenin, quercetin, kaempferol, naringin, and silybonol. The flavonolignans are the active ingredients, and proprietary extracts standardized to 70 percent silymarin are common in Europe.


Milk thistle extract is occasionally used to stimulate the appetite, but its primary use is for liver and gallbladder problems.

Silymarin in proprietary extracts has been shown, through animal research, to have the ability to protect the liver from a range of toxins, including carbon tetrachloride and the deadly poisons from the death-cap Amanita mushrooms.

It is most effective when given six hours before exposure, although there is some benefit up to thirty minutes after exposure to the toxin. Pretreatment with silymarin also protects animals from liver damage due to alcohol.

Silymarin seems to have a membrane-stabilizing activity that prevents toxins from getting into the cells, perhaps by competing for the receptors, or perhaps through antioxidant action and free radical scavenging. It also stimulates the synthesis of ribosomal RNA, an important step in cell regeneration, and inhibits lipid peroxidation.

If silymarin were able only to prevent liver damage from toxins through pretreatment, it would be quite remarkable but of little practical use to a prudent person. In human cases of mushroom poisoning, however, injections of silybin (a component of silymarin) up to forty-eight hours later can reduce the death rate.

Silymarin appears helpful as supportive treatment for chronic liver inflammation from hepatitis or cirrhosis. Some, but not all, clinical studies have shown measurable improvement in liver function tests when silymarin is given to people with alcohol-induced liver damage.

Silybin has also been tested in animals for its ability to protect the kidney from damage due to drugs such as the chemotherapeutic agent cisplatin. Results of this research were promising and should be confirmed by clinical studies in humans.

Silymarin has anti-inflammatory activity and appears to have beneficial effects on T-lymphocytes, possibly enhancing immunity.

Silymarin may slightly reduce the manufacture of cholesterol in the liver and seems to encourage bile excretion.

Bile duct inflammation responds well to treatment with this herb.


Milk thistle should not be administered as a tea or as dried herb because silymarin is neither water-soluble nor readily absorbed from the intestinal tract.

Proprietary products standardized to 70 percent silymarin are utilized in Europe at a usual dose of 420 mg daily.

Treatment normally lasts four to eight weeks at a minimum. Trials of three and six months are common.

One standardized product used in Germany is sold in the United States under the brand name Thisilyn.

Special Precautions

Serious liver diseases require medical attention. In one study, silymarin extract lowered blood glucose and glycosylated hemoglobin values in diabetics.

Diabetic patients should monitor blood glucose closely if they take silymarin, as the dose of insulin or other medication may need adjustment. Please discuss this with your physician.

Adverse Effects

Milk thistle has almost no reported side effects.

Concentrated formulations of silymarin may cause diarrhea or digestive upset in perhaps 1 percent of patients.

Allergic reactions such as hives have been reported very rarely.

Possible Interactions

No adverse interactions have been noted.

It has been suggested that silymarin could be used prophylactically by people taking medicines such as acetaminophen that have the potential to damage the liver. We welcome a clinical trial of standardized silymarin extract to evaluate this theory.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.”.
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