Anni- I assume that is your name

I can only give direct information about cellcept. Because im on it. What i think your doctor may mean by the 'designer drug' was that it may be the less toxic of the two. Thats what I was told, and since Im very sensitive to drugs, they put me on cellcept. It is very expensive, but so far, its kept me from a crisis, and im only on 4-5 months which is right when it kicks in (usually)
I did experience memory loss, mainly short term when the medicine started kicking in, and still do a little bit along with headaches.
Yet my suggestion is that if you are very sensitive to medications, id go with cellcept for it is less toxic than imuran (from my understanding)..
Hope this helps!