There have been at least 11 placebo-controlled studies of kava, involving a total of more than 700 people.13,16,18,38,39,41-43, 55 Most found kava helpful for anxiety symptoms.
One of the best of these was a 6-month, double-blind study that tested kava's effectiveness in 100 people with various forms of anxiety.13 Over the course of the trial, they were evaluated with a list of questions called the Hamilton Anxiety Scale (HAM-A). The HAM-A assigns a total score based on such symptoms as restlessness, nervousness, heart palpitations, stomach discomfort, dizziness, and chest pain. Lower scores indicate reduced anxiety. Participants who were given kava showed significantly improved scores beginning at 8 weeks and continuing throughout the duration of the treatment.
This study is notable for the long delay before kava was effective. Previous studies had shown a good response in one week.14,15,16 The reason for this discrepancy is unclear.
Several double-blind, placebo-controlled studies have specifically tested kava for the treatment of the anxiety that often occurs during menopause.15,16, 38 In one study, 40 women were given either kava plus standard hormone therapy or hormone therapy alone for a period of 6 months. The results showed that women given kava experienced greater improvement in symptoms than those given hormone therapy alone.
However, not all studies have been positive. One double-blind, placebo-controlled study failed to find kava effective for people with generalized anxiety disorder (GAD).39 Another study failed to find kava more effective than placebo for people with both anxiety and insomnia.55
Besides these placebo-controlled studies, one 6-month, double-blind study compared kava against two standard anxiety drugs (oxazepam and bromazepam) in 174 people with anxiety symptoms.18 Improvement in HAM-A scores was about the same in all groups. Another study found kava equally effective as the drugs buspirone and opipramol.^44 ^
A 5-week, double-blind, placebo-controlled trial studied 40 people who had been taking standard anti-anxiety drugs (benzodiazepines) for an average duration of 20 months.17 Participants were gradually tapered off their medications and switched to kava or placebo. Individuals taking kava showed some improvement in anxiety symptoms. This would appear to indicate that kava can successfully be substituted for benzodiazepine drugs. However, participants who were switched from benzodiazepines to placebo showed little to no increase in anxiety, suggesting perhaps that they didn't really need medication after all! Thus, the results of this study are hard to interpret.
Note: This trial involved close medical supervision and very gradual tapering of benzodiazepine dosages. Do not discontinue anti-anxiety medications without supervision. Withdrawal symptoms can be life-threatening.
One study purported to find evidence that kava helps reduce reactions to stressful situations.19 Although, the results mean little because the study lacked a placebo group.
