My INR has been decreasing despite of increased dosage of warfarin. I started on Imuran about 3 months ago and slowly increased to 150 mg/day. The INR change did NOT occur immadiately after taking Imuran. I'm also on 10mg/day Prednisone which will be decreased slowly as the Imuran takes effect. I am now on 6mg/day warfarin. My diet has not changed much so I'm wondering if the Imuran is causing the INR decrease.