Clozapine N-oxide is a major metabolite of clozapine that can be detected in the earliest excretion time interval after clozapine administration [1]. It is produced by the action of cytochrome P450 (CYP) isoforms CYP1A2 and CYP3A4, whose activities, in turn, can be affected by drugs and disease [2]. Clozapine N-oxide is normally biologically inactive. However, it can be used in designer receptor exclusively activated by designer drugs, also known as DREADDs, technology to modulate synthetic receptors in vivo [3].