Kava (Piper methysticum) is a perennial shrub that belongs to the pepper family. It is recognisable by its 5 to 10 inch long heart shaped leaves. However, while the visible parts of the kava plant are interesting from a botanical point of view, nutritionally it is the roots of the plants that can be used medicinally. The roots of the kava plant are thick, tuberous and knotty and can be extensive. The roots by dry weight contain around 45 % starch, 12 % water, 3.5 % simple sugars and 3.5 % protein. In addition the kava root contains around 3.5 % minerals, most of which is potassium. The origins of the kava plant are not known, but it is thought to have been spread through the South Sea Islands by Polynesian explorers in canoes. Kava drinking ceremonies are traditional amongst the Oceanic people (Pacific Islanders) of islands such as Fiji, Samoa and Tonga. These kava ceremonies still form part of the tradition of these islands.
Kava is traditionally used as a treatment for anxiety, and it is believed that the active ingredients that provide some of the anxiolytic effect of kava are chemicals called kavalactones. However, as crude extracts of kava may have better effects against anxiety compared to isolated kavalactones, is is likely that other components within the roots of the kava plant contribute to the medicinal properties. Drinking kava tea made from a decoction of the roots in hot water provides a feeling of contentment and relaxation. Most pharmaceutical anxiolytic drugs work by binding to receptors of the inhibitory neurotransmitter GABA. This then decreases neuronal excitation causing a relating effect. However, kavalactones may work via an alternative route. Animal studies for example show that kavalactone alter receptor domains, and are not able to bind to the GABA receptor. Clinical studies using standardised extracts of kavalactones containing D, L-kavain (a purified kavalactone) have proven effective at treating anxiety in human subjects.
Kavalactone may actually have an effect on the limbic system of the brain, the primitive brain that is thought to be the initiator of emotional feeling. In addition, unlike pharmaceutical drugs, kava does not lose effectiveness over time, and is not associated with side effects at reasonable doses other than the ability to induce sleep (which is not really a side effect). Very high doses of kava over prolonged periods can cause dry skin on the hands and feet, something that is reversible on cessation of kava. Kava can also reduce the sensation of pain, but it does not bind to opioid receptors and so again the mechanisms of action is not clear. The kavalactone content of kava root varies between 3 and 20 percent, and this may affect the neurochemical effects seen. While tablets are available containing kavalactones, it is generally recommended that the whole root is consumed due to the possible anxiolytic contribution of other components in the root.