May be twice in 3 1/2 years. For some reason I don't think I have kidney problems.
I also did twice a parasite cleanse in the same time, this was all just in case. I don't have parasites either, only the first 2 flushes a couple of liverflukes, I think. I had jumped into flushing without knowing much and a few months later I thought that may be I had seen liverflukes since people were talking about it.