Methotrexate-methyl-d3 is a deuterated esterified form of Methotrexate which is an antineoplastic and antirheumatic agent. Studies indicate that Methotrexate-methyl-d3 can act as a folic acid (sc-204758) antagonist. Methotrexate competitively and irreversibly inhibits DHFR (dihydrofolate reductase) which is essential in tetrahydrofolate synthesis. In addition, the reduction in tetrahydrofolate synthesis causes a decrease in purine base synthesis which results in the inhibition of DNA, RNA, thymidylates, and proteins. Alternate studies suggest that Methotrexate-methyl-d3 can suppress T cell activation and adhesion molecule expression through IL-1 suppression..