Studies were conducted to determine the occurrence of liver damage induced by an extract of kava (Piper methysticum) using chronic pre-clinical toxicological tests in rats. Adult male and female Wistar rats were subjected to daily doses of kava extract orally by gavage for 13 weeks. At the end of 13 weeks, the rats were euthanized and blood was collected for laboratory tests. After performing an examination of the thoracic and abdominal cavities, liver resection was performed for macroscopic and histologic examination. Results showed that the P. methysticum extract caused liver lesions in rats and might elicit a toxic effect in humans depending on the dose and period of administration.