Background: Constraints on resources and time often render treatments for anxiety such as psychological interventions impracticable, while synthetic anxiolytic drugs are effective, but are often burdened with adverse events. Options which are effective and safe would be of considerable interest and a welcome addition to the therapeutic repertoire.
Objectives: To assess the effectiveness and safety as reported in rigorous clinical trials of kava extract compared with placebo for treating anxiety.
Search strategy: All publications describing (or which might describe) randomised, double-blind, placebo-controlled trials of kava extract for anxiety were sought through electronic searches on EMBASE, MEDLINE, AMED (British Library), CISCOM (Research Council for Complementary Medicine, London), Central/CCTR and CCDANCTR. The search terms that were used were kava, kawa, kavain, Piper methysticum and Rauschpfeffer (German common name for Piper methysticum). Additionally, manufacturers of kava preparations and experts on the subject were contacted and asked to contribute published and unpublished material. Hand-searches of relevant medical journals (Erfahrungsheilkunde 1996 - 2002, Forsch Komplementärmed Klass Naturheilkd 1994 - 2002, Phytomed 1994 - 2002, Alt Comp Ther 1995 - 2002), conference proceedings (e.g. FACT - Focus on Alternative and Complementary Therapies 1996 - 2002) and our own files were conducted. The searches were updated to August 2002. No restrictions regarding the language of publication were imposed.
Selection criteria: To be included studies were required to be randomised, controlled trials (RCTs), i.e. trials with a randomised generation of allocation sequences, and conducted placebo-controlled and double-blind, i.e. trials with blinding of patients and care providers. Trials using oral preparations containing kava extract as the only component (mono-preparation) were considered. Trials using single constituents of kava extract alone, assessing kava extract as one of several active components in a combination preparation or as a part of a combination therapy were excluded.
Data collection and analysis: Data were extracted systematically according to patient characteristics, interventions and results. Methodological quality of all trials was evaluated using the standard scoring system developed by Jadad and colleagues. The screening of studies, selection, data extraction, validation 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: Eleven trials with a total of 645 participants met the inclusion criteria. The meta-analysis of six studies using the total score on the Hamilton Anxiety scale as a common outcome measure suggests a significant reduction in patients receiving kava extract compared with patients receiving placebo (weighted mean difference: 5.0, 95% confidence interval: 1.1 to 8.8; p = 0.01; n = 345). Adverse events as reported in the reviewed trials were mild, transient and infrequent.
Reviewer's conclusions: Compared with placebo, kava extract appears to be an effective symptomatic treatment option for anxiety. The data available from the reviewed studies suggest that kava is relatively safe for short-term treatment (1 to 24 weeks), although more information is required. Further rigorous investigations, particularly into the long-term safety profile of kava are warranted.