Kava is a member of the pepper family that has long been cultivated by Pacific Islanders for use as a social and ceremonial drink. The first description of kava came to the West from Captain James Cook on his celebrated voyages through the South Seas. Cook reported that on occasions when village elders and chieftains gathered together for significant meetings, they would hold an elaborate kava ceremony. Typically, each participant would drink two or three bowls of chewed kava mixed with coconut milk. Kava was also drunk in less formal social settings as a mild intoxicant.
When they learned about kava's effects, European scientists set to work trying to isolate its active ingredients. However, it wasn't until 1966 that substances named kavalactones were isolated and found to be effective sedatives. One of the most active of these is dihydrokavain, which has been found to produce a sedative, painkilling, and anticonvulsant effect.1,2,3 Other named kavalactones include kavain, methysticin, and dihydromethysticin.
High doses of kava extracts are thought to cause muscle relaxation and even paralysis (without loss of consciousness) at very high doses.4-7 Kava also has local anesthetic properties, producing peculiar numbing sensations when held in the mouth.
The method of action of kava is not fully understood. Conventional tranquilizers in the Valium family interact with special binding sites in the brain called GABA receptors. Early studies of kava suggested that the herb does not affect these receptors.8 However, more recent studies have found an interaction.9,10 The early researchers may have missed the connection because kava appears to affect somewhat unusual parts of the brain.
Note: An accumulation of case reports suggests that kava products may rarely cause severe liver injury, and this has led to a banning of kava by many countries. See Safety Issues for more information.
In 1990, Germany's Commission E authorized the use of kava for relieving "states of nervous anxiety, tension, and agitation," based on evidence from several double-blind studies.13,16,18,38,39 However, case reports of liver damage later led Germany and other countries to ban the sale of kava. See Safety Issues below.
Like other anxiety-reducing drugs, kava could be useful for insomnia, but most of the supporting evidence for this use remains highly preliminary.11,12 One small, double-blind study found that daily use of kava reduced sleep disturbances linked to anxiety.40 However, a larger study failed to find benefits in people with both insomnia and anxiety.55
One animal study suggests that kava may also have value as an aid to alcohol withdrawal.35 (However, individuals who abuse alcohol are probably at increased risk of harm from kava. See Safety Issues.) Kava has been additionally proposed as a treatment for tension headaches, but it has not been evaluated for this purpose.
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.
A typical dosage of kava when used for treatment of anxiety is 300 mg daily of a product standardized to contain 70% kavalactones. A lower dose of 150 mg daily has also been tested, but may be less effective.45,46
The typical dosage for insomnia is 210 mg of kavalactones 1 hour before bedtime.
Until recently, kava had been considered a safe herb. Animal studies have shown that kava dosages of up to 4 times the normal amount cause no health problems, and 13 times the normal dosage causes only mild problems in rats.20 A study of 4,049 people who took a rather low dose of kava (70 mg of kavalactones daily) for 7 weeks found side effects in 1.5% of cases. These were mostly mild gastrointestinal complaints and allergic rashes.21 A 4-week study of 3,029 people given 240 mg of kavalactones daily showed a 2.3% incidence of basically the same side effects.22 One review of the literature concluded that "the data support the safety of kava in treating anxiety at 280 mg kava lactones daily for 4 weeks."47
However, a growing number of case reports have raised serious concerns about kava’s safety. These reports suggest that, occasionally, even normal doses of kava can cause severe liver injury.25, 26,36,37,48-50 Based on these reports, regulatory agencies have taken action in numerous countries banning or restricting sale of kava. However, case reports are notorious for failing to show cause and effect, and some well-regarded experts who have reviewed the literature feel that kava has not been shown to be unsafe.51,52 In a report examining 26 alleged liver toxicity cases in kava users, consuming the herb at the recommended daily dose (less than 120 mg) and duration (less than 3 months) was clearly linked with only one case.56 In all other cases, kava was either not implicated, was taken inappropriately, or was combined with another drug.
At present, if you wish to use this herb, we recommend that you seek physician supervision to monitor for liver inflammation. People with liver problems, who drink alcohol excessively, or who take medications that can harm the liver, are probably at increased risk of harm by kava.
There are other safety concerns as well. For example, kava should not be used by individuals who have had "acute dystonic reactions." These consist of spasms in the muscles of the neck and movements of the eyes, which are believed to be related to effects on dopamine. They are typically caused by antipsychotic drugs, which affect dopamine. Kava might trigger such reactions, too.24
One study suggests that kava does not amplify the effects of alcohol.32 However, there is a case report indicating that kava can increase the effects of certain sedative drugs.33 For this reason, kava probably should not be combined with any drugs that depress mental function. Kava should also not be combined with antipsychotic drugs or drugs used for Parkinson's disease, due to the potential for increased problems with movement.34
The German Commission E monograph warns against the use of kava during pregnancy and nursing. Safety in young children and individuals with kidney disease has not been established.
If you are taking:
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Last reviewed August 2013 by EBSCO CAM Review Board
Last Updated: 8/22/2013