Herbal Fact Sheet: Milk Thistle

Background

• Milk thistle is native to southern Europe, southern Russia, Asia Minor, and northern Africa. It also grows in North and South America and South Australia.
• Silymarin is considered to be the main component of milk thistle seeds, but the terms “milk thistle” and “silymarin” often are used interchangeably.
• Historically, people have used milk thistle for liver disorders, such as hepatitis and cirrhosis, and gallbladder problems.
• Silymarin is the most commonly used herbal supplement in the United States for liver problems.
• Milk thistle products are available as capsules, powders, and extracts.

How Much Do We Know?

• We know little about whether milk thistle is effective in people, as only a few well-designed clinical studies have been conducted.

What Have We Learned?

• Results from clinical trials of milk thistle for liver diseases have been mixed, and two rigorously designed studies found no benefit.
• 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.
• A 2012 clinical trial, cofunded by the National Center for Complementary and Integrative Health (NCCIH) 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.
• Results from a 2013 clinical study suggest that milk thistle may enhance standard treatment in young people with a particular form of anemia (Cooley’s anemia).

What Do We Know About Safety?

• In clinical trials, milk thistle appears to be well tolerated in recommended doses. Occasionally, people report various gastrointestinal side effects.
• Milk thistle may 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).
• Compounds in milk thistle may lower blood sugar levels in people with type 2 diabetes. People with diabetes should use caution.

Keep in Mind

• Tell all your health care providers about any complementary or integrative health approaches you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.