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.8However, 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. SeeSafety 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.40However, 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.