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Milk Thistle

Medically reviewed on June 7, 2018

What is Milk Thistle?

Milk thistle is native to Europe and Asia but now grows wild in North and South America. The plant is 1.5 to 3 m in height and has large, prickly leaves. When broken, the leaves and stems exude a milky sap. The reddish-purple flowers are ridged with sharp spines. The part used as the extract includes the shiny, mottled, black- or grey-toned fruits.

Scientific Name(s)

Silybum marianum (L.) Gaertn., Carduus marianus L, and Mariana mariana.

Common Name(s)

Milk thistle also is known as blessed thistle, bull thistle, fructus cardui mariae, fructus silybi mariae, holy thistle, Lady's milk, Lady's thistle, marian thistle, St. Mary thistle, mild marian thistle, milk thistle, pternix, Silberdistil, silibinin, silybe, silybon, silybum, silymarin, thistle, and thistle of the Blessed Virgin.

What is it used for?

Traditional/Ethnobotanical uses

Milk thistle has been used medicinally since the 4th century BC. Its use in treating liver diseases dates back to the 1700s, and its use to protect the liver can be traced back to Greek references. Pliny the Elder, a 1st century Roman writer (AD 23 to 79), noted that the plant's juice was excellent for "carrying off bile." The 17th century English herbalist Nicholas Culpepper wrote that milk thistle was beneficial in treating jaundice and for removing liver and spleen obstructions. The Eclectic medical system (19th to 20th century) used milk thistle to treat varicose veins, menstrual difficulty, and congestion in the liver, spleen, and kidneys. In homeopathy, a tincture of the seeds has been used to treat liver disorders, jaundice, gallstones, inflammation of the peritoneum, bleeding, bronchitis, and varicose veins. The fruit, stem, and seeds are all considered to have medicinal value. Early colonists introduced milk thistle to North America. The plant was grown in Europe and the de-spined leaves were used in salads and eaten as a vegetable; the stalks and root parts also were consumed. The flower portion was eaten like artichokes. The roasted seeds were used as a coffee substitute.

General uses

Clinical studies of milk thistle are lacking. However, studies suggest a potential use for silymarin, an extract of milk thistle, in treating liver damage from alcoholism, Amanita mushroom poisoning, diabetes, and cancer.

What is the recommended dosage?

Oral consumption of milk thistle (standardized to 70% to 80% silymarin) at 420 mg/day in divided doses is considered safe for up to 41 months, based on clinical trial data. One source suggests 12 to 15 g of drug fruits or 200 to 400 mg of silymarin extract as effective doses. Higher doses of milk thistle have been used in clinical trials.

Contraindications

Allergy to any plant in the daisy family. Avoid use of aboveground parts of the plant in women with breast, uterine, and ovarian cancers, endometriosis, and uterine fibroids.

Pregnancy/Lactation

Avoid use. Information is limited. Use in pregnant and breast-feeding women has been reported in limited clinical studies without any apparent harm, but further data are needed.

Interactions

Milk thistle should be used with caution at high doses.

Side Effects

No serious adverse events have been reported at recommended dosages. The most common effects occurring after oral ingestion included brief GI disturbances.

Toxicology

There are no reports of milk thistle toxicities in humans, and toxicity appears to be low in laboratory animals.

References

1. Milk Thistle. Review of Natural Products. Facts & Comparisons [database online]. St. Louis, MO: Wolters Kluwer Health Inc; December 2013.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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