The National Toxicology Program (NTP) conducted a comprehensive toxicology rodent study comprising a 2-week, 14-week (3 month), and 2-year toxicity and carcinogenicity studies in F344/N rats and B6C3F1 mice to address kava associated liver toxicity and carcinogenicity concerns. The study revealed clear evidence of carcinogenic activity in male mice with some evidence of carcinogenic activity in female mice, and an equivocal evidence of carcinogenic activity among male rats. In addition, kava extract caused increased incidences of tumor-like lesions in eyes, kidneys, liver, pancreas and forestomach in male and female rats, in the liver of male and female mice, and in the forestomach of female mice. In the two-week studies, rats and mice were administered orally 0, 0.125, 0.25, 0.5, 1 and 2 g/kg/d kava extract by gavage. Kava-induced toxicity was observed in the livers of both rats and mice. Dose dependent increases in the absolute and relative liver weights were observed in the 1.0 g/kg and 2.0 g/kg males and in ≥0.5g/kg in female rats.

Yup, that’ll do it lol. Thanks for the link. It is a little over my head in places, but very informative.