Been on imuran for 2 years. A small percentage cannot tolerate it which becomes obvious almost immediately. Others have few side effects and many take it for years.
Until this summer I had no side effects. However, long term users can have blood problems...lowers WBC, RBC and platelets. In other words it can be too effective. My doc has cut the dose from 150 to 75mg and I am being tested every other month. Hopefully, that is all that has to be done. Some patients are able to increase their dosage again after their blood returns to normal levels.
So, if you do tolerate it initially and continue to take it you should have blood tests every 2-3 months to make sure you are OK.
Dosage varies by your body weight and whether or not it is for an AI disease or a transplant.
It has been around for 30+ years and has also been used by transplant patients so doctors have a lot of experience with it. I would not be afraid to give it a try. Most do well on it.
Bill