Kava comes from the root of a shrub that grows in the South Pacific. It is ingested as a tea or in capsule form. The active ingredients are thought to be kavalactones.
(See also Overview of Dietary Supplements.)
Some people in both Europe and the United States who have taken kava developed liver toxicity (including liver failure). Thus, the Food and Drug Administration (FDA) has required a warning label on kava products, and safety is under continuing surveillance. Some researchers believe the liver toxicity may be due to inappropriate preparation or poor quality raw material contaminated with mold that contains liver toxins.
When kava is prepared traditionally (as tea) and used in high doses or over long periods of time, a scaly rash (kava dermopathy), vision problems, changes in blood (such as an increased number of red blood cells), and changes in movement disorders (such as worsening of Parkinson disease) may occur.
The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
National Institutes of Health (NIH), National Center for Complementary and Integrative Health: General information on the use of kava as a dietary supplement