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Herb library · Herb · Silybum marianum

Milk Thistle

A tall purple-flowered thistle whose seed extract (silymarin) is sold mostly for the liver. Trials for liver diseases have been conflicting or too limited to draw conclusions, and product quality varies widely.

Traditional use

Native to Europe and brought to North America by early colonists. Historically milk thistle was used for liver disorders and to increase breast milk. Today it is sold as a supplement for liver disorders, diabetes, and other conditions.

What studies show

  • Limited

    Liver disease: trials in alcohol-related liver disease, hepatitis B and C, fatty liver disease, and liver damage from chemotherapy or toxins have been conflicting or too limited to conclude anything. Two NCCIH-funded trials (hepatitis C, and a progressive fatty liver disease) showed no benefit from silymarin.

  • Limited

    Type 2 diabetes: a small number of studies suggest extracts may help control blood sugar; most were done in Middle Eastern countries, and it is unclear whether results would be the same elsewhere.

  • Insufficient

    Breast milk: it is unclear whether milk thistle affects milk production.

Be careful of

Cautions

  • NoteTaken by mouth it appears well tolerated; the most common side effects are bloating, nausea, and gas. LiverTox reports it has not been implicated in liver injury.
  • NoteProduct quality is a concern: some products contain much more or less silymarin than the label says, or are contaminated with pesticides, microbes, or mold toxins.
  • AllergyIt may cause allergic reactions, especially in people allergic to related plants such as ragweed, chrysanthemum, marigold, and daisy.
  • InteractionIf you take any medicine, check with your clinician first; some herbs and medicines interact in harmful ways.
  • PregnancyLittle is known about its safety in pregnancy or while breastfeeding.
  • Ask a clinicianTalk with a clinician or pharmacist before using this if you take prescription medicines, are pregnant or breastfeeding, or are giving it to a child.

From the old books

What herbals and dispensaries of the past printed. History, in their words.

“Carduus marianus is an old remedy, which had nearly passed out of use and has more recently been revived.”
Harvey Wickes Felter and John Uri Lloyd, King's American Dispensatory (1898), vol. 1, p. 447. See the page of King's American Dispensatory, vol. 1, p. 447 (opens in a new tab) · Read the full passage from King's American Dispensatory, vol. 1, p. 447

Sources

  1. Milk Thistle: Usefulness and Safety (opens in a new tab) · NCCIH · read September 25, 2026
  2. Milk Thistle (LiverTox) (opens in a new tab) · NIH · read September 25, 2026

Reviewed September 25, 2026.