Kava can cause prolongation of anesthesia, sedation, potentiation of the effects of ethanol, barbiturates, and benzodiazepines.  It has also been associated with an increased risk of suicide in patients with depression.  Kava users may also undergo a withdrawal syndrome if the preparation in suddenly discontinued. 

Kava has been primarily used for its sedative properties. Its mechanism of action is similar to that of benzodiazapines and barbiturates. The alpha-pyrone constituents, dihydrokavin and dihydromethycysticin, have weak effects on gamma-aminobutyric acid (GABA) and benzodiazapine receptors. The desired effects of Kava are also those that are responsible for some of the adverse effects and herb-drug interactions.

Kava has been shown to have additive effects when combined with other central nervous system depressants. Almedia and Grimsley reported a case of severe lethargy, disorientation and resultant coma in a patient who ingested Kava. The patient had been taking Alprazolam, Hytrin, and Tagamet without problems until ingesting the Kava. Apparently, it was believed that the Kava had an additive effect with the Alprazolam, a benzodiazapine. Kava should never be combined with any other sedative, central nervous system depressant, or alcohol.

Hepatotoxicity appears to be another risk with Kava use. As of September 2001, 18 cases of Kava-Kava induced liver failure had been reported to the European regulatory authorities. Most of the literature about liver toxicity from Kava is found in European literature, however, currently the FDA is asking physicians to report  any suspicious cases of hepatotoxicity or liver failure due to a number of suspected cases reported in the U.S.

Kava use has also been reported to be associated with causing extrapyramidal side effects, usually seen in patients taking antipsychotic medications. It has also been thought to worsen Parkinson’s disease due to a possible blockade of the effects of dopamine. Schelosky et al. reported on four cases where the patients began taking Kava, doses ranging from 100 to 450 mg per day, and began having extrapyramidal side effects within 90 minutes, after four hours, after four days and after ten days. Extrapyramidal side effects included oral and lingual dyskinesia, torticollis, painful twisting trunk movements, oculogyric crisis and exacerbation of Parkinson’s disease.  Kava should never be used by patients who suffer from Parkinson’s disease or are taking prescription antipsychotic medication.