Kawa, awa, intoxicating pepper, rauschpfeffer, sakau, tonga, yagona
Botanical Name / Family
Piper methysticum (family Piperaceae)
Plant Parts Used
Root and rhizome
The most important constituents responsible for the pharmacological activity of kava rhizome are the fat-soluble kava lactones (kavapyrones), mainly methysticin, dihydromethisticin, kavain, dihydrokavain and desmethoxyangonin and flavonoids (flavokavains).
For many centuries, Pacific Islanders have used the kava kava root to prepare a beverage used in welcoming ceremonies for important visitors. Drinking kava is not only done to induce pleasant mental states but also to reduce anxiety and promote socialising. It is believed that the first report about kava came to the West from Captain James Cook during his voyages through the Pacific region.
Kava Kava: Main Actions
The kava lactones reach a large number of targets that influence CNS activity. They interact with dopaminergic, serotonergic, GABA-ergic and glutamatergic neurotransmission, seem to inhibit monoamine oxidase B and exert multiple effects on ion channels, according to in vitro and in vivo research. Additionally, animal studies show that kava lactones are chiefly responsible for these effects that give rise to many of the herb’s clinical actions.
Although the exact mechanism of action is not yet understood, it has been observed that sleep promotion may be due to the preferential activity of D,L-kavain and kava extract on the limbic structures and, in particular, the amygdalar complex in the brain.
In an EEG brain-mapping study it was demonstrated that D,L-kavain could induce a dose-dependent increase in delta-, theta- and alpha-1 power, as well as a decrease in alpha-2 and beta power. These results indicate a sedative effect at the higher dose range.
A recent study showed that kava extract produces a statistically significant dose-dependent anxiolytic-like behavioural change in rat models of anxiety. The effect is not mediated through the benzodiazepine binding site on the GABA-A receptor complex, as flumazenil, a competitive benzodiazepine receptor antagonist, did not block this effect.
ANALGESIC AND LOCAL ANAESTHETIC
Both the aqueous and lipid-soluble extracts of kava exhibit antinociceptive properties in experimental animal models. The effect is not mediated by an opiate pathway, as naloxone does not reduce the effects when administered in doses that reverse the effects of morphine. More recently, in vitro research has identified several compounds found in kava that have the ability to inhibit COX-1 and to a lesser extent COX-2 enzyme activities.
The local anaesthetic effect of kava is well known for topical use and has been described as similar to procaine and cocaine.
Antispasmodic activity for skeletal muscle has been observed in vitro and in vivo for both kava extract and kava lactones. In vivo research suggests that kavain impairs vascular smooth muscle contraction, likely through inhibition of calcium channels.
Kava Kava: Other Actions
Although in vitro studies published in 2002 suggested whole kava extract and kavalactones have widespread inhibitory effects on various cytochrome enzymes, such as CYP3A4, more recent in vivo tests found no effects on CYP3A4/5, CYP1A2 or CYP2D6, but did demonstrate significant inhibition (approximately 40%) of CYP2E1.