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 Milk Thistle 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 Milk Thistle 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, powders, and tinctures.
What the Science Says
- Laboratory studies suggest 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. Results from clinical trials of milk thistle for liver diseases have been mixed, and most studies have not been rigorously designed. Reviews of the research have concluded that the efficacy of milk thistle against liver disease has not been established, and additional, high-quality trials are needed.
- The Hepatitis C Antiviral Long-Term Treatment Against Cirrhosis (HALT) study, sponsored by NIH, found that silymarin use by hepatitis C patients was associated with fewer and milder symptoms of liver disease and somewhat better quality of life, but there was no change in virus activity or liver inflammation.
- NCCAM-funded research includes a number of studies on milk thistle for liver disease, such as a phase II trial to better understand the use of milk thistle for chronic hepatitis C. A study cofunded by NCCAM and the National Institute of Diabetes and Digestive and Kidney Diseases is examining the effects of milk thistle on people with chronic hepatitis C who have not responded to conventional antiviral treatment, and people with nonalcoholic steatohepatitis (liver disease that occurs in people who drink little or no alcohol).
- The National Cancer Institute is studying the effectiveness of silymarin for patients with leukemia who experience chemotherapy-related liver damage. The National Institute of Nursing Research is investigating whether milk thistle is an effective treatment for hepatitis C in people with both hepatitis C and HIV.
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.
- 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.
- Milk thistle. Natural Medicines Comprehensive Database. Accessed at www.naturaldatabase.com on October 7, 2009.
- 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.