Sorry to hear your Lupus is active again. I've been on Imuran for 9 years now. The drug has definitely been around for a long time, and has been used for Lupus for many, many years.
I've had tremendous success with it, and the only side effect I have is a slight drop in white blood cells, and a very slight increase in my liver enzymes. Everything is within normal ranges though. Some people get upset stomach and some hair loss during the early stages of being on it and then those go away. Some people also don't do well on it. Whether it's Cellcept or Imuran, you just have to try one out and see how you do. The reactions are different for every person.