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Preparations from kava (Piper methysticum) have been banned based on the suspicion of adverse liver effects. To date, no convincing proof has been given to substantiate the danger of a relevant toxicity.

Kava and kava derived products are generally considered as very safe. In 2002, the German health authorities banned kava extract containing products based on the suspicion of a potential liver toxicity, as derived from adverse event reports. From the case reports and the sales figures of kava extracts, an incidence rate of one potential case in 60 to 125 million patients was deducted. Clinical, pre-clinical and toxicological studies have so far failed to show toxicity for kava preparations and their constituents.

Kava (Piper methysticum) and kavalactones were recently suspected to be the
cause of drug induced hepatitis. Our in vitro screening was aimed on the detection
of cytotoxic effects of differently produced kava extracts and isolated kavalactones
in liver cells. Methods: Kava root powder, an ethanolic full extract, an acetonic special extract and the six major kavalactones (kavain, dihydrokavain, methysticin, dihydromethysticin, yangonin and desmethoxyyangonin) were tested in primary cultured rat hepatocytes and human HepG2 cells using cytotoxicity assays including the MTT test.
Download Cytotoxicity of Kava Extracts and Kavalactones in Primary Cultured Rat Hepatocytes and Human HepG2 cells Poster: 53rd Annual Congress of the Society for Medicinal Plant Research, Florence (Italy), August 21-25, 2005