From the sounds of the Wikipedia article (part of which reproduced below), it would appear that it has some definite intoxicating effects.
Kava or kava-kava (Piper methysticum) (Piper: Latin for 'pepper', methysticum: (Latinized) Greek for 'intoxicating') is a crop of the western Pacific.
The name kava(-kava) is from Tongan and Marquesan; other names for kava include ʻawa (Hawaiʻi), ava (Samoa), yaqona (Fiji), and sakau (Pohnpei).
The roots of the plant are used to produce a drink with sedative and anesthetic properties. Kava is consumed throughout the Pacific Ocean cultures of Polynesia, including Hawaii, Vanuatu, Melanesia and some parts of Micronesia. Kava is sedating and is primarily consumed to relax without disrupting mental clarity. Its active ingredients are called kavalactones. A Cochrane Collaboration systematic review of its evidence concluded it was likely to be more effective than placebo at treating short-term social anxiety. Safety concerns have been raised over liver toxicity, largely due to the use of stems and leaves by supplement makers, as opposed to solely the root of the plant as dictated by traditional uses. However, based on a retrospective study of retained P. methysticum drug materials in Germany, the alkaloid pipermethystine, occurring to about 0.2% in the leaves, is an unlikely cause for the observed hepatotoxicity. Whether kava hepatotoxicity may be due to contamination with aflatoxins or other mould hepatotoxins, requires further studies. Heavy use of kava with comorbid alcohol consumption or an existing liver condition appears to lead to malnutrition, weight loss, liver damage (causing elevated serum γ -glutamyl transferase and high-density lipoprotein cholesterol levels), renal dysfunction, rashes, pulmonary hypertension, macrocytosis of red cells, lymphocytopenia, and decreasing platelet volumes.http://en.wikipedia.org/wiki/Kava
Keeping in mind that substances such as meth-amphetamine, cocaine, marijuana and a whole raft of other substances are not mentioned in the suttas, we use our judgement, as well as the counsel of our wise companions, in understanding what falls within the precept. If it were me, I would give the kava tea a wide bearth.
“No lists of things to be done. The day providential to itself. The hour. There is no later. This is later. All things of grace and beauty such that one holds them to one's heart have a common provenance in pain. Their birth in grief and ashes.”
- Cormac McCarthy, The Road
Learn this from the waters:
in mountain clefts and chasms,
loud gush the streamlets,
but great rivers flow silently.
- Sutta Nipata 3.725Compassionate Hands Foundation
(Buddhist aid in Myanmar) • Buddhist Global Relief