Naftopidil-d5 is deuterium labeled Naftopidil. Naftopidil (KT-611) is is a selective alpha1-adrenoceptor antagonist, with Kis of 3.7 nM, 20 nM and 1.2 nM for the cloned human α1a-, α1b- and α1d-adrenoceptor subtypes, respectively. Naftopidil has antiproliferative effects. Naftopidil can be used for the research of prostate hyperplasia[1][2].