I've been on Imuran generic Azathioprene since 2007, between 100-125mg/day with zero evident side effects. Bumped to 150mg/day in February due to a flare, and after 3 months began to see additional hair loss, though I'm not going bald yet, thank goodness!
I also tend to get a lot of tiny 'micro cycsts' as I call them, which look like little bumps or skin-colored pimples around my chest and neck and upper arms, but my mother has them too, and i believe that's more heredity in my case. I did have skin tags in some areas prior to starting the Azathioprene, and they cleared completely after about a year on the meds.
Hair loss can be attributed to other causes, though - thyroid issues, for example, or even stress... My last few months of college my hair was falling out in gobs, and it scared the hell out of me - but I was preparing to graduate, and under a lot of stress, and once i graduated, the fallout stopped. Being diagnosed with Crohn's, or having a flare, can also be stressful on its own, so consider that as well.
Good luck!