The opioid receptor μ 1 (OPRM1) gene, located on chromosome 6q24-q25 [72], is responsible for encoding the μ opioid receptor, which has been implicated in respiration, gastrointestinal motility, physical dependence, euphoria, and analgesia [66]. In-depth study of this gene has identified several single nucleotide polymorphisms (SNPs) that are associated with opioid dependence and with ethnic variation in opioid dependence [72].
