Kavain is the active ingredient of extracts of Kava root ((Piper methysticum).

For millennia, Pacific Islanders have been using the root of a native pepper plant called kava (Piper methysticum) to prepare a non-alcoholic psychoactive beverage, which is also called kava. Kava drinking is an integral component of the Pacific Islander culture, with kava playing roles as a sacred drug in religious rituals, a social lubricant at formal gatherings, and a medicine to induce relaxation and sleep."

Source :PLoS ONE, 0157700 .

It has been extensively investigated by Western medicine, and has been found to be very effective at controlling anxiety. It has also been used as an anti-convulsant (for treating Epilepsyplugin-autotooltip__plain plugin-autotooltip_bigEpilepsy

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To date, there is no solid explanation of the pharmacological mechanism(s) which make it effective.

Despite the long history of kava consumption and the wealth of clinical evidence in favour of the efficacy of kavalactones in treating anxiety, there is a severe gap in our understanding of the molecular target(s) and the mechanism(s) of action of these psychoactive compounds."

[ source as above ]

Further info : Icahn School of Medicine at Mount Sinai.