4'-fluoro-4-methylaminorex 4'-fluoro-4-methylaminorex 4'-fluoro-4-methylaminorex (4-fpo) is a recreational designer drug from the substituted aminorex family, with stimulant effects. it was first detected in slovenia in 2018. it was made illegal in italy in march 2020. 4'-fluoro-4-methylaminorexidentifiers iupac name 4-methyl-5-(4-fluorophenyl)-4,5-dihydro-1,3-oxazol-2-amine cas number1364933-64-1 ypubchem cid134080816chemspider78231362uniiqmw9x4b373chemical and physical dataformulac10h11fn2omolar mass194.209 g·mol−13d model (jsmol)interactive image smiles fc1ccc(cc1)c1oc(n)=nc1c inchi inchi=1s/c10h11fn2o/c1-6-9(14-10(12)13-6)7-2-4-8(11)5-3-7/h2-6,9h,1h3,(h2,12,13)key:uykywishpdedrq-uhfffaoysa-n