depends on the kind of kava. 2 heaping teaspoons of Mahakea micro at once on an empty stomach gets me pretty messed up for a couple hours, but almost never gets me nauseous. when i've tried doing multiple bits of it, I end up not feeling as strong of an effect, and, ironically, it's more likely to get me sick.
I take the 2 heaping teaspoons, eat a little something like 10 minutes later, then wait for 4-6 hours before repeating the process, up to 3 times per day. For me, this dosage regiment is really consistent in the effects and lack of nausea. If I drink an energy drink, or even coffee during the day, it could throw me off - making effects more intense and the possibility of nausea worse, because Kava accentuates the effects of caffeine.
I like to time it so I take my last dose around 6pm, any later and it seems to interfere with my sleep. I have the last kava at 6, play some sports with friends, and by around 11 i'm ready for sleep. I make sure not to ever have caffeine after 3 pm or so.