Milk Thistle 

This fact sheet provides basic information about the herb milk thistle—common 

names, uses, potential side effects, and resources for more information. Milk thistle 

is a flowering herb that is native to the Mediterranean region. It has been used for 

thousands of years as a remedy for a variety of ailments, especially liver problems. 

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 

What It Is Used For 

Milk thistle is believed to have protective effects on the liver and improve its 

function. It is typically used to treat liver cirrhosis, chronic hepatitis (liver 

inflammation), and gallbladder disorders. Treatment claims also include: 

•	 Lowering cholesterol levels 

•	 Reducing insulin resistance in people with type 2 diabetes who also 

have cirrhosis 

•	 Reducing the growth of cancer cells in breast, cervical, and prostate cancers. 

How It Is Used 

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, and infusions (strong teas). 

What the Science Says 

•	 There have been some studies of milk thistle on liver disease in humans, but 

these have been small. Some promising data have been reported, but study 

results at this time are mixed. 

•	 Although some studies conducted outside the United States support claims of 

oral milk thistle to improve liver function, there have been flaws in study design 

and reporting. To date, there is no conclusive evidence to prove its claimed uses. 

•	 Recent NCCAM-funded research includes a phase II study to better 

understand the use of milk thistle for chronic hepatitis C. Additional 

research, cofunded by NCCAM and the National Institute of Diabetes and 

Digestive and Kidney Diseases, includes studies of milk thistle for chronic 

hepatitis C and nonalcoholic steatohepatitis (liver disease that occurs in 

people who drink little or no alcohol). 

•	 The National Cancer Institute and the National Institute of Nursing Research 

are also studying milk thistle for cancer prevention and to treat 

complications in HIV patients. 
 

 

 

 

 

Side Effects and Cautions 

•	 In clinical trials, milk thistle generally has few side effects. Occasionally, people report a 

laxative effect, upset stomach, diarrhea, and bloating. 

•	 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). 

•	 Tell your health care providers about any complementary and alternative practices you 

use. Give them a full picture of what you do to manage your health. This will help ensure 

coordinated and safe care. 

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. 01­

E024. Also accessible at http://www.ahrq.gov/clinic/epcsums/milktsum.htm. 

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 http://www.naturaldatabase.com on July 3, 2007. 

Milk thistle (Silybum marianum), silymarin. Natural Standard Database Web site. Accessed at 

http://www.naturalstandard.com on June 28, 2007. 

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 and Complementary and Alternative Medicine: 2003 

Update. National Center for Complementary and Alternative Medicine Web site. Accessed at 

http://nccam.nih.gov/health/hepatitisc/ on July 5, 2007. 

For More Information 

Visit the NCCAM Web site at nccam.nih.gov and view: 

•	 What’s in the Bottle? An Introduction to Dietary Supplements at nccam.nih.gov/health/bottle/ 

•	 Herbal Supplements: Consider Safety, Too at nccam.nih.gov/health/supplement-safety/

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

CAM on PubMed 

Web site: nccam.nih.gov/camonpubmed/ 

NIH Office of Dietary Supplements 

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

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 

♦♦♦

U.S. Department of Health and Human Services 

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Created September 2005 

Updated March 2008 

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