According to some estimates, up to a quarter of us will experience significant anxiety at some time in our lives. When we do, we will probably be prescribed drugs such as benzodiazepines. Unfortunately, these drugs can have serious side effects such as dependence and memory impairment. Some non-pharmacological treatments are available. These include psychological interventions. People with anxiety also use other types of therapy. One plant-based option is kava extract. A new Cochrane review brings together the evidence from randomised trials to investigate the effectiveness of this and looks at whether it too has adverse side effects.

Kava is prepared from the root of a pepper plant. It has been used in countries in the South Pacific for both recreational and medicinal purposes for some time. Recently, it has become increasingly common as a herbal remedy in the northern hemisphere.

The Cochrane reviewers did the usual extensive searching. They looked for double blind, placebo controlled, randomised trials in databases such as EMBASE and MEDLINE, databases dedicated to complementary medicine and The Cochrane Library. Relevant journals were gone through by hand. Requests for published and unpublished trials were sent to manufacturers of kava preparations and other people who might be expected to know of relevant studies.

Fourteen eligible reports were found. But, on closer inspection, seven of these were excluded. Two were duplicate publications of studies that were to be included, three used kavain rather than kava extract, and patients in the seventh excluded trial were given benzodiazepine as well as kava or its placebo. The remaining seven randomised trials — all of which had been published — were included in the review. These seven trials included a total of 377 patients.

Each of the trials found a statistically significant reduction in anxiety among the patients allocated to kava. However, only three of the trials reported data that were suitable for a statistical analysis. These included the largest single trial, which had randomised 100 patients, along with two smaller ones of 40 and 58 patients respectively. The pooled result shows a highly significant reduction in anxiety.

The reviewers conclude that their results show that kava extract is more effective than placebo. The adverse side effects reported in the trials were not common and were mild. So, on balance, kava may be a worthwhile treatment for people with anxiety. However, the reviewers are also cautious in their interpretation. Their review is based on a relatively small amount of randomised evidence. It is possible that they failed to find some null, or even negative, unpublished trials that could have an important impact on their results and conclusions. They suggest that further and more rigorous research is still needed to assess the balance of benefits and harms of kava. Further Information

The relevant Cochrane review is: Pittler M, Edzard E. Kava extract for treating anxiety (Cochrane Review). In: The Cochrane Library, Issue 4, 2001. Oxford: Update Software.

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November 2001