What is Milk Thistle?

What is Milk Thistle?

This section is compiled by Frank M. Painter, D.C.
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Thanks to the University of North Carolina School of Pharmacy for the use of this article!

Michelle Giesler and Kimberly Jones

General Description

  • Other names: Marian thistle, St. Mary's thistle, Our Lady's thistle
  • Family: Asteraceae
  • Distribution: Native to the Mediterranean region of Europe, but naturalized in California and the eastern US

Description of plant:

  • tall herb with prickly leaves and a milky sap
  • Small, hard fruits (achenes), a feathery tuft or pappus is removed
  • Milk white veins in the leaves (originated in the milk of the Virgin Mary which once fell upon the plant)

Parts used:

  • ripe fruit (not seeds), root, leaves, hull

Chemical composition

  • Silymarin- chemical mixture of antihepatotoxic principles; 1-4% conc. in fruit
  • Shown to consist of a large number of flavonolignans, including principally silybin accompanied by isosilybin, dehydrosilybin, silydianin, silychristin, etc.

History and folk use

  • Formerly frequently cultivated in gardens
  • The stalks may be eaten and are palatable and nutritious
  • Young leaves may be eaten as a salad, and were sometimes baked in pies
  • The heads were formerly boiled and eaten, treated like those of an Artichoke
  • Thought to be a great breeder of milk and proper diet for nursing women
  • Thought to have a healing property in those with snake bites
  • If worn around the neck it would protect you from snake bites
  • Fruit formerly thought to cure hydrophobia
  • Applied externally, said to have been proven beneficial in cases of cancer
  • The young, tender plant be boiled and eaten in the spring as a blood cleanser
  • Fruits have been used for many years for a variety of conditions, especially liver complaints. However, medicinal use of the plant, except as a simple bitter, was practically discontinued early in the twentieth century.

Primary effects in the body

  • Acts on cell membranes of liver cells to prevent the entry of toxic substances
  • Stimulates protein synthesis, accelerating regeneration process & production of liver cells
  • Acts as an antioxidant, with far greater free radical damage control than vitamin E
  • It may offer some protection against toxic side effects from acetaminophen

Clinical applications

  • Early treatment for chronic liver problems
  • Rehabilitation from alcohol, solvent or IV recreational abuse
  • Protects hepatocytes from heavy metal, chemical and alcohol injury
  • Limits fatty degeneration and speeds up hepatitis recovery, slowing or reversing cirrhosis
  • Supportive treatment for inflammatory liver conditions and cirrhosis


  • None reported

Drug and disease interactions

  • None reported


  • Fruit (seeds): 2-3 capsules up to 3 x day
  • Tincture: 1:5, 60% alcohol, ½ to 1 teaspoon up to 4 x day (equal parts of root & seed with hull attached)
  • Silymarin is very poorly soluble in water so is not effective as a tea (< 10% plant activity)
  • Poor solubility and poor absorption from GI tract (20-50%) make active principles best administered parenterally
  • Oral use requires a concentrated product
  • Capsules containing 200mg of a concentrated extract representing 140mg of silymarin

Primary and Tertiary literature

Protection from Amanita phalloides intoxication Tox Appl Pharm 73 (1984)

  • Severe poisoning with mortality rate of 30%
  • Study in beagles
  • 50 gm/kg silibinin 5 and 24 hrs post-intoxication
  • 4 deaths in control group / 0 deaths with silibinin
  • Reduction in elevations of GPT, GOT, AP and bilirubin with silibinin; less decrease in PT
  • Mechanism of Action?
    • Modification or occupance of cell membrane receptor sites
    • Decrease phospholipid metabolism
    • Prevention of inhibition of RNA Polymerase and RNA synthesis by toxin

Increase of Glutathione Content in the Liver Planta Medica 55 (1989)

  • 200 mg/kg silymarin single dose
  • Over 50% increase GSH in liver and intestine
  • Selectivity
    • accumulation principally in liver
    • entero-hepatic recirculation
  • An increase in GSH can increase conjugation/elimination of toxins and decrease lipid peroxidation
  • Mechanism of action?
    • Increase in membrane permeability of amino acids involved in GSH synthesis

Stimulation of DNA synthesis in malignant cell lines? Biochem Pharm 35(1986)

  • 27 mg/kg silibinin prior to injection of radioactive thymidine
  • Silibinin increases ribosomal RNA synthesis
  • No influence on DNA synthesis in normal livers
  • Large increase in DNA synthesis in hepatectomized rats / 23-35% increase in thymidine incorporation
  • No influence on DNA synthesis in fast growing hepatoma cell cultures
  • Mechanism of action?
    • Hepatectomized rats
      • If the regulatory signal for replication initiation is given, increase in rRNA and protein synthesis also accelerates DNA synthesis
    • Hepatoma cells
      • The rate of proliferation is already maximal and cannot be further intensified

Effect of silibinin on biliary lipid composition Journal of Hepatology 12(1991)

  • The rats
    • 100mg/kg or 50mg/kg silymarin for 7 days
    • measured biliary cholesterol, biliary phospholipid, total bile salt and bile flow
    • decrease in biliary cholesterol and phosolipid
    • no change in bile flow and total bile salts
  • The Humans
    • 400mg/day silymarin in cholecystectomized and gallstone patients for 1 month
    • significant decrease in biliary cholesterol for both groups
  • Mechanism of Action?
    • Found a dose dependent decrease in HMG-CoA reductase in the liver with increasing silymarin concentration
    • A decrease in HMG-CoA reductase leads to a decrease in synthesis of cholesterol


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