in the Pacific, only the root of the plant is used. Demand skyrocketed to the point that unscrupulous producers in the West started using stems and peelings, which don't have much kavalactone content, anyway, but apparently do have chemicals that cause liver toxicity.
http://en.wikipedia.org/wiki/Kava#Toxicology_of_pill_form_kava_extracts_with_stems_and_leavesHawaiian researchers learned from a trader in Fijian kava that European pharmaceutical companies eagerly bought up the stem and leaves peelings when demand for kava extract soared in Europe in 2000 and 2001. Before 2002, substantial amounts of aerial parts of the kava plant were being exported to North America and Europe and obviously used for the production of commercial pill extracts. For traditional use in the South Pacific, stem peelings and leaves are discarded, and only the rhizomes are used and extracted with water. This may explain why native populations that make heavy use of kava experience side effects that are mild, temporary, and confined to the skin, whereas industrialized countries that have newly adopted kava occasionally show severe, acute responses.:dunce:
edit: spelling