Kava extracts are popular in Europe and have been investigated in numerous clinical trials, primarily in European countries. As a result, many research papers have been published in languages other than English. In order to provide a more complete description of the evidence available, secondary sources have been used where necessary.
A 2000 Cochrane review of the scientific literature assessed the results from seven, double-blind, randomised placebo-controlled trials and concluded that kava extract has significant anxiolytic activity and is superior to placebo for the symptomatic treatment of anxiety. An update of this review was published in 2003 and analysed results from 12 clinical studies involving 700 subjects. The results of 7 studies that used the Hamilton Anxiety Scale (HAM-A) score were pooled and a significant reduction in anxiety was observed for kava treatment compared with placebo. The results of the five studies that were not submitted to meta-analysis largely support these findings. The extract most commonly tested was WS 1490 at a dose of up to 300 mg daily. Preliminary evidence suggests it may be equivalent to benzodiazepines for non-psychotic anxiety.
According to the authors of the review, none of the trials reported any hepatotoxic events and seven trials measured liver enzyme levels as safety parameters and reported no clinically significant changes.
MENOPASUAL AND PERIMENOPASUAL ANXIETY
A randomised placebo-controlled study conducted with 40 menopausal women found that using kava extract, together with HRT, led to significant reductions in anxiety, as measured by the HAM-A scale at both 3- and 6-month follow-up.
A 3-month, randomised, open study of 68 perimenopausal women showed that treatment with kava (100 mg/day) significantly reduced anxiety (P < 0.001) at 1 month and 3 months. This was significantly greater than that spontaneously occurring in controls (P < 0.009).
GENERALISED ANXIETY DISORDER
An 8-week randomised, double-blind, multicentre clinical trial involving 129 outpatients with GAD showed that kava kava LI 1 50 (400 mg/day) was as effective as buspirone in the acute treatment of GAD, with about 75% of patients responding to treatment.
Comparative studies suggest the absence of significant differences between benzodiazepines and kavain or kava extract as treatments for anxiety. A 1993 double-blind comparative study involving 174 subjects over 6 weeks demonstrated that 300 mg/day of a 70% kava lactone extract produced a similar improvement in anxiety level, as measured by HAM-A scores, to 15 mg oxazepam or 9 mg bromazepam taken daily. D,L-kavain produced equivalent anxiolytic effects to oxazepam in 38 outpatients with neurotic or psychosomatic disturbances, under double-blind study conditions.
Kava may have a role in reducing anxiety and improving subjective wellbeing during benzodiazepine withdrawal, according to a 2001 randomised, double-blind, placebo-controlled study. During the first 2 weeks of that study, kava dose was increased from 50 mg to 300 mg/day while benzodiazepine use was tapered off during the same period. Kava extract was superior to placebo in reducing anxiety as measured by the HAM-A scale and improved subjects’ feelings of wellbeing according to a subjective wellbeing scale (Bf-S total scores).
Lack of tolerance
The results from a randomised, double-blind trial conducted over 25 weeks have found that physical tolerance does not develop to kava kava extract and it is well tolerated. Evidence from a randomised double-blind study conducted with 84 patients has shown that treatment with kavain (one of the active constituents of kava kava) produces continuous improvements in parameters such as memory function, vigilance, fluency of mental functions and reaction time. Interestingly, these effects were reported over a relatively short period of 3 weeks. Another randomised double-blind trial conducted with 52 patients over 28 days not only confirmed anxiolytic activity but also found that kavain promoted subjective vitality-related performance.
Commission E approves the use of kava in conditions of nervous anxiety and restlessness.
The hypnotic activity of kava extract was confirmed in a RCT in which a single dose of 300 mg kava extract was found to improve the quality of sleep significantly. In vivo experiments with D,L-kavain have shown that it reduces active wakefulness and significantly prolongs sleep, compared with placebo.
Kava Kava: Other Uses
Traditionally, the herb has been used to treat urinary tract infections, asthma, conditions associated with pain, gonorrhoea and syphilis, and to assist with weight reduction, muscle relaxation and sleep. Topically, it has been used as a local anaesthetic and to treat pruritus.
Kava Kava: Dosage Range
- Cut rhizome: 1.7-3.4 g/day.
- Dried rhizome: 1.5-3 g/day in divided doses or equivalent to 60-120 mg kavapyrones daily.
- Fluid extract (1:2): 3-8.5 mL/day in divided doses.
- Ideally, ethanolic extracts should contain > 20 mg/mL kava lactones.
ACCORDING TO CLINICAL STUDIES
- Anxiety: generally doses up to 300 mg daily of kava extract WS 1490 providing 105-210 mg kavalactones. A kava extract LI 1 50 (400 mg/day) was used successfully in generalised anxiety disorder.
- Insomnia — a single dose of 300 mg kava extract.
- Benzodiazepine withdrawal — 300 mg/day of kava extract.