Previous findings indicate that Oprm1 regulation and opioid system activity contribute to MA consumption in mice (Belknap et al., 2013; Eastwood et al., 2018; Eastwood and Phillips, 2014a; Eastwood and Phillips, 2014b), and MA dependence/psychosis in humans (Ide et al., 2004; Ide et al., 2006). The gene discussed is OPRM1; the disease is psychotic disorder.