MOA: a folic acid antagonist that INHIBITS CYTOKINE PRODUCTION and PURINE NUCLEOTIDE BIOSYNTHESIS, leading to immunosuppressive and anti-inflammatory effects (response occurs after 3-6 WEEKS OF Tx) LOW DOSE: DMARDs HIGH DOSE: Anti Cancer A/E: MUCOSAL ULCERATION & nausea, cytopenias (low WBC count), liver cirrhosis, ACUTE PNEUMONIA-LIKE SYNDROME (IN CHRONIC USE)