I can tell you first hand about liver troubles from kava. I was using it a few times a week, but in large doses and it was chilling me out very nicely.
Then it started making me feel weird and slightly off. My doc is a holistic doc and he told me to lay off because my liver count was much higher.
However, in small doses, it's really effective for anxiety or stress, especially in combo with st.john's wort.
