OPRM1 and opiate dependence: The opioid receptor system has also been demonstrated to be upregulated in cocaine users (151), detoxified alcoholic patients (152, 153) and opioid dependence (154) when assessed with the selective mu-opioid receptor (MOR) agonist radioligand [11C]carfentanil and is a target of opioid antagonist medication to prevent relapse.