Kava (piper methysticum) products are banned over here in many european countries because there were some 40 known cases where the use of pharmaceutical kava kava products may have been a factor in severe liver damage. Research seems to iindicate that it may have to do with what part of the plant has been used and the dosage. I came across the ceremonial use of this plant in social anthropology classes and I have consumed it once years ago in this context. It tasted like drinking a spoonful of mud diluted in a glass of water and it makes the tip of your tongue go slightly numb. It has a certain mood elevating ability, reduces inhibitions and from what I remember, it had (although mildly) some carateristics associated to doing a drug or drinking.
Aside of the health contoversy about liver damage that has not been completely solved yet, I wouldn't recommend to use it regularly over an extended period of time. In fact, from how I experienced it, I wouldn't recommend it to anyone who has dealt with any form of addiction to be honest, since it is mood altering and there is a potential for abuse in my opinion.