I have been on methotrexate for a few months for seronegative arthritis. I am now currently on 15mg and haven't had any side effects, except for caffeine like headaches. I have always been pretty sensitive to caffeine, but now I am like ultra sensitive. Guess should bite the bullet and just quit. So my question is, I have read methotrexate does cause a buildup of adenosine, and if so how much does caffience affect the efficacy of the drug? Thanks,