i am also on methotexate - it can cause liver problems (dont know about kidney) however, my doc told me that it is suppose to help with joint pain and swelling as well as other things...used for some cancers, psorisis (sp?), arthritis, and some other things so i dont understand your use of tylenol arthritis. My doc told me not to take aspirin with it but that tylenol was ok - maybe you should call your doc back to get you questions answered.