Kava beverages, made from dried roots of the shrub Piper methysticum, have been used ceremonially and socially in the South Pacific for hundreds of years and in Europe since the 1700s.
Several well-conducted human studies have demonstrated kava's efficacy in the treatment of anxiety with effects observed after as few as one to two doses and progressive improvements over one to four weeks. Preliminary evidence suggests possible equivalence to benzodiazepines.
Many experts believe that kava is neither sedating nor tolerance-forming in recommended doses. Some trials report occasional mild sedation, although preliminary data from small studies suggest lack of neurological-psychological impairment.
There is growing concern regarding the potential for liver toxicity from kava. Multiple cases of liver damage have been reported in Europe, including hepatitis, cirrhosis, and liver failure. Kava has been removed from shelves in several countries due to these safety concerns. The U.S. Food and Drug Administration (FDA) has issued warnings to consumers and physicians. It is not clear what dose or duration of use is correlated with the risk of liver damage. The quality of these case reports has been variable; several are vague, describe use of products that do not actually list kava as an ingredient, or include patients who also ingest large quantities of alcohol. Nonetheless, caution is warranted.
Chronic or heavy use of kava has also been associated with cases of neurotoxicity, pulmonary hypertension, and dermatologic changes. Most human trials have been shorter than two months, with the longest study being six months in duration.