Milk Thistle

© Steven Foster

This fact sheet provides basic information about milk thistle—

common names, what the science says, potential side effects and 

cautions, and resources for more information.

Common Names—milk thistle, Mary thistle, holy thistle. Milk thistle 

is sometimes called silymarin, which is actually a mixture of the herb’s 

active components, including silybinin (also called silibinin or silybin).

Latin Name—Silybum marianum

Milk thistle is a flowering herb native to the Mediterranean region. It has 

been used for thousands of years as a remedy for a variety of ailments, and 

historically was thought to have protective effects on the liver and improve 

its function. Today, its primary folk uses include liver disorders such as 

cirrhosis and chronic hepatitis, and gallbladder disorders. Other folk uses 

include lowering cholesterol levels, reducing insulin resistance in people 

who have both type 2 diabetes and cirrhosis, and reducing the growth of 

breast, cervical, and prostate cancer cells.

Silymarin, which can be extracted from the seeds (fruit) of the milk thistle 

plant, is believed to be the biologically active part of the herb. The seeds are 

used to prepare capsules, extracts, powders, and tinctures.

What the Science Says 

Previous laboratory studies suggested that milk thistle may benefit the 

liver by protecting and promoting the growth of liver cells, fighting 

oxidation (a chemical process that can damage cells), and inhibiting 

inflammation. However, results from small clinical trials of milk thistle 

for liver diseases have been mixed, and two rigorously designed studies 

found no benefit. 

• A 2012 clinical trial, cofunded by NCCAM and the National Institute 

of Diabetes and Digestive and Kidney Diseases, showed that two 

higher-than-usual doses of silymarin were no better than placebo 

for chronic hepatitis C in people who had not responded to 

standard antiviral treatment. 

• The 2008 Hepatitis C Antiviral Long-Term Treatment Against 

Cirrhosis (HALT-C) study, sponsored by the National Institutes of 

Health (NIH), found that hepatitis C patients who used silymarin had 

fewer and milder symptoms of liver disease and somewhat better 

quality of life but no change in virus activity or liver inflammation.
Side Effects and Cautions 

• In clinical trials, milk thistle appears to be well tolerated in recommended doses. Occasionally, people 

report various gastrointestinal side effects.

• Milk thistle can produce allergic reactions, which tend to be more common among people who are allergic 

to plants in the same family (for example, ragweed, chrysanthemum, marigold, and daisy).

• Milk thistle may lower blood sugar levels. People with diabetes or hypoglycemia, or people taking drugs or 

supplements that affect blood sugar levels, should use caution.

• Tell all your health care providers about any complementary health practices you use. Give them a full 

picture of what you do to manage your health. This will help ensure coordinated and safe care. For tips 

about talking with your health care providers about complementary and alternative medicine, see 

NCCAM’s Time to Talk campaign at nccam.nih.gov/timetotalk/. 

Sources

Agency for Healthcare Research and Quality. Milk Thistle: Effects on Liver Disease and Cirrhosis and Clinical Adverse Effects. Evidence Report/

Technology Assessment no. 21. Rockville, MD: Agency for Healthcare Research and Quality; 2000. AHRQ publication no. 01-E025.

Fried MW, Navarro VJ, Afdhal N, et al. Effect of silymarin (milk thistle) on liver disease in patients with chronic hepatitis C who failed 

interferon therapy: a randomized, placebo-controlled trial. JAMA. 2012;308(3):274-282.

Ladas E, Kroli DJ, Kelly KM. Milk thistle (Silybum marianum). In: Coates P, Blackman M, Cragg G, et al., eds. Encyclopedia of Dietary 

Supplements. New York, NY: Marcel Dekker; 2005:467-482.

Milk thistle. Natural Medicines Comprehensive Database. Accessed at www.naturaldatabase.com on October 7, 2009.

Milk thistle (Silybum marianum), silymarin. Natural Standard Database Web site. Accessed at www.naturalstandard.com on October 7, 2009.

Milk thistle fruit. In: Blumenthal M, Goldberg A, Brinckman J, eds. Herbal Medicine: Expanded Commission E Monographs. Newton, MA: 

Lippincott Williams & Wilkins; 2000:257-263.

National Center for Complementary and Alternative Medicine. Hepatitis C: A Focus on Herbal Supplements. National Center for 

Complementary and Alternative Medicine Web site. Accessed at nccam.nih.gov/health/hepatitisc/hepatitiscfacts.htm on July 18, 2012. 

Rambaldi A, Jacobs BP, Gluud C. Milk thistle for alcoholic and/or hepatitis B or C virus liver diseases. Cochrane Database of Systematic 

Reviews. 2007;(4):CD003620.

Seeff LB, Curto TM, Szabo G, et al. Herbal product use by persons enrolled in the hepatitis C antiviral long-term treatment against 

cirrhosis (HALT-C) trial. Hepatology. 2008;47(2):605-612.

For More Information

Visit the NCCAM Web site at nccam.nih.gov and view Using Dietary Supplements Wisely (nccam.nih.gov/health/supplements/wiseuse.htm).

NCCAM Clearinghouse

Toll-free in the U.S.: 1-888-644-6226

TTY (for deaf and hard-of-hearing callers): 1-866-464-3615

E-mail: info@nccam.nih.gov

PubMed®

Web site: www.ncbi.nlm.nih.gov/sites/entrez

NIH Office of Dietary Supplements

Web site: www.ods.od.nih.gov

NIH National Library of Medicine’s MedlinePlus

Milk Thistle Listing: www.nlm.nih.gov/medlineplus/druginfo/natural/138.html

This publication is not copyrighted and is in the public domain. Duplication is encouraged.

NCCAM has provided this material for your information. It is not intended to substitute for the medical expertise and advice of your 

primary health care provider. We encourage you to discuss any decisions about treatment or care with your health care provider. The 

mention of any product, service, or therapy is not an endorsement by NCCAM.

National Institutes of Health

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U.S. Department of Health and Human Services

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Created September 2005

Updated July 2012