Kava extract for treating anxiety.

BACKGROUND: Synthetic anxiolytic drugs are effective for anxiety, but are often burdened with adverse events. Constraints on resources and time often render treatments such as psychological interventions impracticable. Thus, an effective and safe oral medication would be of considerable interest and a welcome addition to the therapeutic repertoire.

OBJECTIVES: To systematically review the evidence from rigorous clinical trials assessing the efficacy and safety of kava extract versus placebo for the treatment of anxiety.

SEARCH STRATEGY: Publications describing randomised controlled trials (RCTs) of kava extract for anxiety were sought through Medline, Embase, Biosis, AMED, CISCOM and the Cochrane Library (all from their respective inception to June 1998). The search terms used were kava, kawa, kavain, Piper methysticum and Rauschpfeffer (German common name for Piper methysticum). Manufacturers of kava preparations and experts on the subject were contacted and asked to contribute published and unpublished material. In addition, our own files were searched and the bibliographies of all of the studies identified were scanned for further trials. There were no restrictions on the language of publication.

SELECTION CRITERIA: Randomized, double-blind trials of oral kava extract mono-preparations for the treatment of anxiety were included. Trials comparing kava with placebo were included. Trials assessing kava as one of several active components in a combination preparation or as a part of a combination treatment were excluded.

DATA COLLECTION AND ANALYSIS: All publications were blinded prior to assessment by a person not involved in the study. Data were extracted systematically. Methodological quality of all trials was evaluated using the standard scoring system developed by Jadad and colleagues. The screening of studies, selection, data extraction and the assessment of methodological quality were performed independently by the two reviewers. Disagreements in the evaluation of individual trials were resolved through discussion.

MAIN RESULTS: Seven trials met the inclusion criteria. All of the reviewed trials suggest superiority of kava extract over placebo. The meta-analysis of three studies using the Hamilton Anxiety Score as a common outcome measure suggests a significant differential treatment effect in favour of kava extract (weighted mean difference: 9.7, 95% confidence interval: 3.5 - 15.8). Adverse events as reported in the reviewed trials were mild, transient and infrequent.

REVIEWER'S CONCLUSIONS: The evidence presented implies that kava extract is superior compared with placebo and relatively safe as a treatment option for anxiety. These findings warrant further and more rigorous investigations into the efficacy and safety of kava extract.