A University of Hawaii professor says he may have isolated the link between kava extracts and liver damage that has led to a ban on kava products in some countries.
Chang Shih Tang, professor of molecular biosciences and biosystems engineering, says a compound found in stem peelings and leaves of the plant has proved toxic to human livers.
Professor Tang says, however, there is still no evidence that the kava root, used by traditional drinkers, causes liver damage.
"My hope is that more people engage in this research, to clear the name of kava as a traditional drink ....The kava peelings, or the above ground parts, are not a part of the traditional....I think my research is based on the belief that if the product's been used for all these years, it should be safe."
Professor Tang says stem peelings have been sold in the past to pharmaceutical companies and he suspects they are used in some herbal supplements.
Last year some European countries, Canada, the United States, Australia and New Zealand banned products with kava extracts.
This had a serious impact on the export of kava from the Pacific.