I was Imuran for 4 months and was recently taken off of it, due to getting started on Remicade. The only real side effect I had with Imuran was thinning hair.
Anyhow, my GI decided to move me to Remicade during my last flare. I believe the Imuran would have worked for me after time--however, I am a slow metabolizer so it takes longer for that drug to start working. My GI didn't want to waste any more time and wanted to get the flare under control. Also, I had been on prednisone for a long time and he wanted to get me off of it.
I personally think it is a good idea to give Imuran a try. It's a lot less expensive than Remicade.