Kava Kava root was originally used as a religious drink by various island tribes of Oceania.

It's now used as a relaxant, both by people who have anxiety problems, insomnia, and people who simply want to calm down. It often produces a calming effect.
However, if used excessively for more than a month, yellow skin will result.
Also, if used enough, your body will go numb. Kavateens, the main chemical in Kava Kava is a numbing agent.