COMT and opioid use disorder: This study aimed to explore the potential association between the catechol-O-methyltransferase (COMT) rs4680 and mu-opioid receptor (OPRM<sub>1</sub>) rs1799971 genotypes and XR-NTX treatment outcomes in patients with opioid use disorder (OUD) specifically focusing on treatment retention, relapse to opioids, number of days of opioid use, and opioid cravings.