Pharmacokinetic and pharmacodynamic drug interactions with Kava (Piper methysticum Forst. f.).

Kava kava, a beverage or extract prepared from the rhizome of the kava plant (Piper methysticum Forst. f.), was used for many centuries as a traditional beverage in the Pacific Islands. During the past few decades, kava has also gained popularity in Western countries as well, due to its anxiolytic and sedative properties. However, in recent years, kava has been implicated in several liver failure cases which led to its ban in many countries and this has prompted wide discussion on its relative benefits and risks as a social beverage and a herbal remedy. Recently, it has been shown that several kavalactones, the assumed active principles of kava extracts, are potent inhibitors of several enzymes of the CYP 450 system (CYP1A2, 2C9, 2C19, 2D6, 3A4 and 4A9/11). This indicates that kava has a high potential for causing pharmacokinetic drug interactions with other herbal products or drugs, which are metabolised by the CYP 450 enzymes. In addition, several pharmacodynamic interactions have been postulated and indeed observed. Nevertheless, evidence of true pharmacokinetic and/or pharmacodynamic interactions remains unsubstantiated, and only few investigations of the potential of kava preparations to interact with specific drugs have been carried out. This review provides a critical overview of the existing data on interactions of kava with other drugs and concludes that there is an urgent need for further in vitro and in vivo investigations to fully understand clinically significant interactions with kava that have the potential to cause adverse effects or toxicity in kava users.