Fentanyl, a potent synthetic opioid analgesic approximately 50–100 times more potent than morphine, has recognized addictive potential and induces pronounced euphoria through activation of the μ-opioid receptor (MOR) and associated reward pathways (Vardanyan and Hruby, 2014; Volkow et al., 2019). This evidence concerns the gene OPRM1 and Euphoria.