Milk thistle contains a group of flavonoids, or chemical compounds, collectively called silymarin. In theory, silymarin repairs damaged liver cells, reduces swelling and acts as an antioxidant, protecting new cells from damage.
A 2005 study published in the "American Journal of Gastroenterology" indicated that milk thistle extract had no significant effect on patients who had either hepatitis B or C or who suffered from alcoholic liver disease. MayoClinic.com adds that as of 2010, more research is necessary before recommending milk thistle as a treatment for either alcoholic cirrhosis or viral hepatitis. The National Cancer Institute cannot recommend the herb for cancer due to the lack of research.
The U.S. Food and Drug Administration has not approved milk thistle as a treatment for liver conditions or any other medical problem. Consult a physician before using milk thistle.