What Is Milk Thistle?

Milk thistle, also known as St. Mary's thistle, has been used as an herbal remedy for more than 2,000 years. According to the University of Maryland Medical Center, it is used as a supplement for kidney, liver and gall bladder issues. Its healing properties are believed to be tied to antioxidants and flavonoids that have anti-inflammatory benefits.

The plant

Indigenous to the Mediterranean, milk thistle grows in dry, sunny regions worldwide. The plant can grow up to 10 feet tall within a year, producing reddish-purple flowers and wide leaves with white spots. When you crush the leaves, they release milklike, white sap, hence the name milk thistle. Because the plant spreads quickly, some consider milk thistle to be a weed. The seeds hold the healing component called silymarin, a group of three flavonoids.

Mushroom poisoning

Milk thistle has been used traditionally as an antidote to deathcap mushroom poison. In animal studies, milk thistle has been shown to completely eliminate the mushroom's toxic effects when administered within 10 minutes. Even within 24 hours, it can still reduce the risk of death or liver damage.


According to WebMD, milk thistle can improve diabetes when used as part of a combination treatment with traditional methods. It is said to decrease blood sugar levels, aid insulin resistance and improve cholesterol in type 2 diabetes patients.

Cancer studies

In test-tube studies, silymarin and other milk thistle substances appear to shorten the life span of cancer cells by inhibiting them from reproducing and dividing. Preliminary studies also point toward its use as sunscreen protection to lower skin cancer risks.


Animal studies have shown that silymarin might protect the liver from the effects of drugs like acetaminophen by growing new liver cells, thereby repairing damage. Human studies, however, have been inconclusive. The same goes for using milk thistle as a treatment for alcoholic cirrhosis and hepatitis. Regardless of the ambiguous results in studies, milk thistle is often used as treatment for these liver problems.


Milk thistle products usually contain 70 to 80 percent of silymarin in standardized preparation that are made from the seeds. You can buy this supplement in the form of capsules, liquid extract, tinctures and as a silymarin phosphatidylcholine complex. The latter is thought to be absorbed more easily than regular milk thistle.

Side effects, interactions and precautions

Like other supplements, side effects depend on the individual but are generally considered mild, consisting of diarrhea and stomach upset.

Milk thistle might interfere with drugs for allergies and cholesterol, as well as with antianxiety medications, blood thinners and some cancer drugs. Also, check with your doctor if you are taking antipsychotics, seizure medication, hormone replacement drugs or birth control pills.

Avoid milk thistle when breastfeeding or while pregnant. Also, do not take it if you have a history of hormone-related cancer or if you are allergic to marigolds, ragweed, chamomile, daisies, chrysanthemums or yarrow.

You should always discuss the use of milk thistle and all other herbal supplements with your health care professional, even if none of these factors apply.

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