I've been on azathioprine for Crohns disease for nearly 2 weeks at 100mg (going up to 150mg tomorrow) and two days ago I started coming down with a cold, it is developing and today I feel pretty rotten. Until now I have been cold/infection free for about a year and a half and I am wondering if the cold is related to my immune system reducing from the drug. What I would like to know is how long it takes for azathioprine to start lowering the immune system and could after 2 weeks my immune system be lowered enough to start being more susceptible? Hope someone can help.