Milk Thistle

Silybum marianum

Milk thistle is a flowering plant that grows throughout the world, usually in dry sunny areas. Its name refers to the milky white sap that comes from the leaves when crushed. An extract from the seeds has been used medicinally for centuries for a variety of health problems, particularly those affecting the liver, kidney, and gallbladder. A compound called silymarin is one of the substances in milk thistle believed to help protect the liver from toxins. Silymarin has antioxidant and anti-inflammatory effects that may help the liver repair itself after being damaged by toxins.

Used for:

Milk thistle is used by herbalists to treat liver diseases including acute and chronic hepatitis, alcoholic cirrhosis and nonalcoholic steatohepatitis (NASH), as well as liver damage caused by chemicals, poisoning by the mushroom Amanita phalloides, jaundice and chronic inflammatory liver disease. Despite these traditional uses, the Natural Medicine Comprehensive Database (NMDB) found milk thistle to be “possibly ineffective for hepatitis B and C.  NMDB notes there is “insufficient evidence that milk thistle is effective for treating many liver disorders including alcoholic liver disease, hepatitis, and toxin-induced liver damage as well as mushroom poisoning, chemotherapy toxicity, diabetic nephropathy and some neurological diseases like multiple sclerosis and Alzheimer’s disease.

Milk thistle is also used to treat for loss of appetite, heartburn (dyspepsia), and seasonal allergies and has been rated as “possibly effective by the NMCD for treatment of seasonal allergies and for treatment of indigestion in a combination product that includes peppermint leaf, German chamomile, caraway, licorice, clown’s mustard plant, celandine, angelica, and lemon balm.  The NMCB notes that milk thistle is “likely effective in reducing menopausal symptoms including hot flashes and night sweats by approximately 70% when used in combination with extracts of black cohosh, dong quai, red clover, American ginseng, and chasteberry.  The silymarin constituent (200 mg three times daily for 4 months) may help improve diabetes by improving insulin sensitivity and reduce fasting blood glucose in combination with conventional therapy.

Available in:

Capsules, tablets liquid extract, tinctures and silymarin phosphatidylcholine complex.

Herb / drug interactions:

The breakdown of milk thistle by certain liver enzymes may interfere with the action of drugs that are metabolized by those same enzymes. It may lead to hypoglycemia when combined with diabetes medications such as glimepiride (Amaryl).  These include the allergy drug fexofenadine (Allegra); statins to lower cholesterol; anti-anxiety drugs including alprazolam (Xanax) diazepam (Valium), and lorazepam (Ativan); blood thinning drugs (antiplatelets and anticoagulants) including clopidorgrel (Plavix) and warfarin (Coumadin); and some cancer drugs like Tamoxifen. In addition, milk thistle may interact with antipsychotics including butyrophenones (such as haloperidol) and phenothiazines (such as chlorpromazine, fluphenazine, and promethazine). It may also interfere with phenytoin (Dilantin) used for seizures, halothane, used during general anesthesia, as well as birth control pills and hormone replacement therapy.

Other safety concerns:

While milk thistle is generally regarded as safe, it may cause side effects including mild stomach upset and diarrhea, indigestion, intestinal gas, bloating, fullness or pain and loss of appetite. Its safety hasn’t been established for women who are pregnant or breastfeeding. Touching the plant can sometimes cause a rash. If you’re allergic to ragweed, chrysanthemums, marigolds, chamomile, yarrow or daises, you may develop an allergic reaction to milk thistle. Because extracts from the milk thistle plant can act like estrogen, women should avoid them if they have estrogen-related conditions including uterine fibroids, endometriosis or a history of hormone-related cancers (breast, uterine, ovarian). Extracts from milk thistle seeds do not have estrogenic effects.

When buying:

Look for extracts of milk thistle with silybum or silymarin standardized to 70 to 80 percent.


Take two capsules of a standardized extract two or three times a day or as the label directs. You can stay on milk thistle indefinitely, although this is not generally recommended.

Child dosage:

No evidence shows that milk thistle is safe for children.

Dr. Weil says:

I recommend taking extracts of the seeds of milk thistle for liver problems including acute and chronic hepatitis and alcoholic cirrhosis. Another liver problem that is becoming chronic in the wake of the obesity epidemic in North America is nonalcoholic steatohepatitis, also known as fatty liver disease, in which fatty infiltration of the liver leads to inflammation and scarring. Milk thistle is nontoxic, and European research shows that it stimulates regeneration of liver cells and protects them from toxic injury. It can also be useful in reducing allergy symptoms and indigestion.  You can find milk thistle at most health food stores under the names silymarin or silybum.

Reviewed by Raneth Heng, M.D., December 14th, 2015.

Milk Thistle. University of Maryland Medical Center,, accessed April 20, 2014

Milk Thistle. Natural Medicine Comprehensive Database (Consumer Version),, accessed April 14, 2014

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