Protein arginine methyltransferases (PRMTs) are critical epigenetic regulators involved in diverse cellular processes. Among them, PRMT5 produces symmetric dimethyl arginine (SDMA) and plays essential roles in RNA splicing, DNA damage repair, and cell cycle control. By modifying both histone and non-histone proteins, PRMT5 has been implicated in oncogenesis, and its frequent overexpression in cancers underscores its value as a therapeutic target. Several small-molecule PRMT5 inhibitors have been developed, including GSK3326595, EPZ015666, JNJ64619178, and LLY-283, but these compounds exhibit distinct mechanisms of action. Specifically, GSK3326595 and EPZ015666 act as substrate-competitive inhibitors, whereas JNJ64619178 and LLY-283 function as dual-competitive inhibitors targeting both S-adenosylmethionine and substrates. This mechanistic divergence is further supported by differences in their amino acid interaction profiles within the PRMT5 catalytic pocket. Furthermore, through screening of an FDA-approved drug library, we identified a novel PRMT5 inhibitor that induces dose-dependent reductions in PRMT5-mediated methylation, including SDMA, H3R8me2s, and H4R3me2s. These findings suggest that this compound may be repurposed as an anticancer agent, thereby broadening the therapeutic scope of PRMT5 inhibition.