Kavalactones are the main psychoactive components of the roots of Piper methysticum (kava), a shrub common on some Pacific Ocean islands. Another class of compounds found in P. methysticum are the Flavokawains, which are substituted chalcones in nature and not lactones, and thus they are not kavalactones.
The rhizome and roots of the shrub are ground, grated and steeped in water to produce a non-alcoholic drink which is said to promote sociability, mental clarity, and reduction of anxiety (see main kava entry). The quantity and ratio of kavalactones present vary dramatically and are highest when roots are extracted with solvents rather than by conventional tea preparation (but note safety issues; see kava).
Some use lipids to aid in kavalactone extraction. (ie; whole milk, oils, etc.)
At least 18 different kavalactones have been identified to date, with Methysticin being the first identified. The Flavokawains are not kavalactones and as such are not included in the table below, which only lists natural kavalactones that have been identified in P. methysticum (and thus does not include pharmacologically interesting synthetic analogues, such as ethysticin).
Effects of kavalactones include mild sedation, a slight numbing of the gums and mouth, and vivid dreams. Kava has been reported to improve cognitive performance and promote a cheerful mood.  Muscle relaxant, anaesthetic, anticonvulsive and anxiolytic effects are thought to result from direct interactions of kavalactones with voltage-gated ion channels.  Research currently suggests that kavalactones potentiate GABAA activity but do not alter levels of dopamine and serotonin in the CNS.  Heavy, long-term kava use does not cause any reduction of ability in saccade and cognitive tests but is associated with elevated liver enzymes. 
The United States Food and Drug Administration (FDA) has warned that very rare cases of liver damage or fulminant liver failure may be caused by kava-containing supplements. However, these injuries might result from pipermethystine, an alkaloid present in portions of the plant used industrially but normally discarded in traditional preparations (see kava).
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