Milk Thistle

Scientific Name:  Silybum marianum

Also Known as: Marian thistle, Blessed thistle

Parts Used:  Seeds, whole plant

Native to: The Mediterranean area 

Some Traditional Uses: Liver protector

Current Medicinal Uses and Purposes: Liver support--treatment for hepatitis, jaundice, cirrhosis, diabetes, fetal alcohol syndrome, and removing toxins from alcohol, ultraviolet radiation, poisons, food additives, pollution, and prescription and illegal drugs. Also used to treat amanita mushroom poisoning. Research suggests some ability to prevent or reduce internal damage and side effects due to chemotherapy and radiation. Herbalists point to benefits for cardiovascular and kidney disease.

Side Effects and Contraindications: No negative drug interactions known so far. Nontoxic. High doses may have a laxative effect. Mild allergic reaction possible from contact with plant.

Areas of Further Research: Milk thistle's ability to help with bronze diabetes; itching associated with cholestasis during pregnancy; side effects of the Alzheimers drug Tacrine; cancer; cancer drug resistance. In addition, milk thistle seems to positively potentiate some cancer drugs.

Listen to two different Plant Detective radio shows on Milk Thistle! Part I and Part II


Photo by Rose Cooper, courtesy of Rose Cooper and the Texas Agricultural Experiment Station of Uvalde

Some call it noxious weed. Others see it as powerful medicine.

Even though it's a terribly invasive weed, milk thistle has been recognized since ancient times as a remarkable liver protectant. It has other good effects as well, some of which need more research. Find out more on this page.


The helpful natural chemicals in milk thistle are mainly in its seeds (which are really its fruits).

The principle constituent in milk thistle, silymarin, helps restructure liver cells to prevent toxins from penetrating the liver and stimulates the regenerative ability of the liver to help form new cells. Milk thistle holds promise for liver-related diseases like hepatitis, cirrhosis, diabetes, and fetal alcohol syndrome. 

Milk thistle is so helpful to the liver, its compounds are some of the only substances that can save people who eat the most poisonous mushrooms in the world, Amanita phalloides, pictured below.

Photo by Benjamin Wolfe

Milk thistle also fights prostate and skin cancer, and has benefits for people with other types of cancer. It makes some cancer drugs work better and can prevent side effects of chemotherapy and radiation.

Studies show that milk thistle protects against ultraviolet radiation from the sun. 

Milk thistle was brought to North America from its native home in the Mediterranean. Once it got to North America, it spread and made trouble for farmers. In some states--Washington and California, for example--it's against the law to plant milk thistle. 

Milk thistle is one of the best-selling medicinal herbs in the United States. 

"Our Lady of Guadaloupe"  Artist: Mary B. Kelly

What's in a Name?

Milk thistle's name comes from its white, milky sap and from belief in past times that it helped the flow of breast milk in new mothers. The plant has long been associated with Mary, the mother of Jesus--an association seen in milk thistle's scientific name. It's said, for example, that the white markings on milk thistle's leaves (seen below) were caused by a drop of Mary's milk.

Photo courtesy of


Milk Thistle References for The Plant Detective Radio Show

Abascal, Kathy, and Eric Yarnell. "The Many Faces of Silybum marianum (Milk Thistle)."Part 1–Treating Cancer and Hyperlipidemia and Restoring Kidney Function." Alternative and Complementary Therapies Aug 2003: 170-75.

Abascal, Kathy, and Yarnell, Eric. "The Many Faces of Silybum marianum (Milk Thistle): Part 2–Clinical Uses, Safety, and Types of Preparations." Alternative and Complementary Therapies Oct 2003: 251-56.

Castleman, Michael. "Liver Let Live: A Natural Remedy for Liver Disease Has Been Ignored by Mainstream Medicine." Mother Jones Nov/Dec 1997; 22(6): 25.

Grauds, Constance. "Milk Thistle: A Potential Life-Saver." Pharmacy Times Mar 1996: 95.

Hobbs, Christopher. "Milk Thistle Therapy: An Herbal Defense Against Everyday Toxins." Herbs for Health Jul/Aug 1997: 47-49.

Jones, Cindy LA. "Milk Thistle Compound May Prevent Skin Cancer." Herbs for Health Sept/Oct 1997: 72.

Keville, Kathi. "Herbs That Love Your Liver: Enhance the Health of This Vital Organ." Vegetarian Times Aug 1996, no. 228: 72.

Lahiri-Chatterjee, Moushumi, Santosh K. Katiyar, Rajiv R. Mohan, and Rajesh Agarwal. "A Flavonoid Antioxidant, Silymarin, Affords Exceptionally High Protection against Tumor Promotion in the SENCAR Mouse Skin Tumorigenesis Model." Cancer Research Feb 1999; 59: 622-32.

"Milk Thistle.", 12/7/06.

Nielka, PH van Erp, Sharyn D. Baker, Ming Zhao, Michelle A. Rudek, Henk-Jan Guchelaar, Johan WR Nortier, Alex Sparreboom, and Hans Gelderblom. "Effect of Milk Thistle (Silybum marianum) on the Pharmocokinetics of Irinotecan." Clin Cancer Res 2005; 11(21): 7800-5.
Rainone, Francine. "Milk Thistle." American Family Physician Oct. 1, 2005; 72(7): 1285-88.

Review of Natural Products. "Milk Thistle." St Louis, MO: Facts and Comparisons, Jan 1997.

Rohrer, W. Jean. "Milk Thistle.", 7/9/99.

Swerdlow, J. L.  2000. Nature's Medicine.  National Geographic Society, Washington, D.C.

Thorne Research. "Silybum marianum (Milk Thistle)" (monograph). Alternative Medicine Review 1999, 4(4): 272-74.

Washington State Noxious Weed Control Board. Written Findings for Class A Weeds: "Milk Thistle.", 9/28/2006.

Yarnell, Eric. Email communication about "Plant Detective" milk thistle scripts, August 20, 2006.