Kava (Piper methysticum) – Botany, Therapeutic Uses, Constituents, Pharmaco, Adverse Effects

In the autumn of 1835, Charles Darwin traveled from the Galapagos Islands to Tahiti during his five year voyage on the HMS Beagle. He describes in his journal a walking tour of Tahiti with local guides. Besides viewing stands of wild sugar cane, Darwin notes seeing kava growing at the edge of a small creek. He recognized this plant from a description provided by Johann Forester, the botanist who accompanied Captain James Cook on the HMS Endeavour on an earlier expedition to the South Pacific. Forester named the plant Piper methysticum. The species designation was derived in part from the Greek word methi, meaning strong drink. Knowing this, Darwin tasted the plant stem. He described the flavor as acrid and unpleasant. However, it is the root of the kava that is typically consumed for its central nervous system effects. These purportedly include a relief from anxiety, a feeling of tranquility, and somnolence. Usually the root is macerated or ground and an aqueous extract served as a drink. Alternatively, the unprepared root is chewed.

A native of tropical islands, the precise geographical origin of kava, the discovery of its psychoactive properties, and the development of its use are unknown as written records on these subjects date only from the eighteenth century when the British first arrived in Oceania. As its ingestion causes noticeable and generally pleasant changes in the sensorium, it was undoubtedly used by South Sea island natives for centuries before the arrival of Europeans. Evidence for this is that both Captain Cook and Darwin found the locals consuming kava as part of well-established social and religious ceremonies. Today kava beverages are still used for social events in Tonga, Samoa, and Fiji. While once generally available in the Americas and Europe as an herbal supplement, the use of kava is now restricted because of reports linking it to severe liver toxicity. In fact, safety concerns led to its ban in several countries, including France and Switzerland.

As kava products are marketed as anxiolytics and hypnotics, the active constituents, thought to be kavalactones, appear to be central nervous system depressants akin to ethyl alcohol, the barbiturates, and the benzodiazepines. The kavalactones of particular interest are desmethoxyyangonin and kavain because of the evidence they may influence neurotransmitter activity in the brain. It is unknown whether the central nervous system effects of kava are solely attributable to kavalactones or to other plant constituents as well.