(See also Overview of Dietary Supplements.)
Kava comes from the root of a shrub (Piper methysticum) that grows in the South Pacific. It is ingested as a tea or in capsule form. Active ingredients are thought to be kavalactones.
A 2003 Cochrane review evaluated 11 trials (total of 645 participants) to assess the effectiveness and safety of kava extract in clinical trials for treating anxiety. The meta-analysis concluded that kava extract appears to be an effective option for relieving anxiety compared to placebo (1). This study also concluded that consumption of kava supplements for 1 to 24 wk appeared safe but suggested a need to study long-term safety. It is unclear how the supplements used in the meta-analysis above was standardized. Standardization of kava supplements to the active ingredient kavalactones (3 to 20%) should be included in future clinical trials.
Since 1999 several cases of liver toxicity (including liver failure) in both Europe and the US after taking kava have prompted the FDA to mandate a warning label on kava products (2). Safety is under continuing surveillance.
When kava is prepared traditionally (as tea) and used in high doses (> 6 to 12 g/day of dried root) or over long periods (up to 6 wk), there have been reports of scaly skin rash (kava dermopathy), blood changes (eg, macrocytosis, leukopenia), and neurologic changes (eg, torticollis, oculogyric crisis, worsening of Parkinson disease, movement disorders).