methylthiouracil methylthiouracil methylthiouracil is an organosulfur compound that is used antithyroid preparation. it is a thioamide, closely related to propylthiouracil. methylthiouracil is not used clinically in the united states, it has a similar mechanism of action and side effect to that of propylthiouricil. the drug acts to decrease the formation of stored thyroid hormone, as thyroglobulin in the thyroid gland. the clinical effects of the drug to treat the hyperthyroid state can have a lag period of up to two weeks, depending on the stores of thyroglobulin and other factors. methylthiouracilclinical dataahfs/drugs.cominternational drug namesatc codeh03ba01 (who) identifiers iupac name 6-methyl-2-thioxo-2,3-dihydropyrimidin-4(1h)-one cas number56-04-2pubchem cid667493chemspider580871uniiqw24888u5fkeggc19265 ychemblchembl1330588comptox dashboard (epa)dtxsid2020890 echa infocard100.000.230 chemical and physical dataformulac5h6n2osmolar mass142.18 g·mol−13d model (jsmol)interactive image smiles cc1=cc(=o)nc(=s)n1 inchi inchi=1s/c5h6n2os/c1-3-2-4(8)7-5(9)6-3/h2h,1h3,(h2,6,7,8,9)key:hwgbhcrjgxageu-uhfffaoysa-n (verify) synthesis methylthiouracil synthesis: methylthiouracil is prepared quite simply by condensation of ethyl acetoacetate with thiourea. further work in this series shows that better activity was obtained by incorporation of a lipophilic side chain.