How effective is imuran (azathioprine) for crohn's disease?

Generally effective: Azathioprine (imuran) works by decreasing the white blood cell (WBC) count. Wbc's are responsible for fighting infections, as well as for causing inflammation in crohn's disease. Azathioprine can often effectively lower the WBC count enough to stop the inflammation from crohn's disease without causing many infections. It is important to monitor the WBC count while on azathioprine.

Sometimes: Imuran (azathioprine) seems to be effective in a small subset of patients with Crohn's (likely fewer than 40%). At the moment it's difficult to predict who will respond in the long term. But as it can be safely used with monitoring, it's often worth trying.