We sought to provide an overview of opioid dependence including epidemiology and genetic susceptibility and we summarized the evidence for genes most commonly associated with opioid dependence. These genes related to dopamine and opioid receptors, and neurotrophic factors (Table 1). The majority of the studies reviewed were retrospective, case-control studies that compared genotype and allele frequencies between cases of opioid dependence and controls. These studies often excluded individuals with any major psychiatric disorders (Axis 1 disorders) and polysubstance use, and a significant portion of study participants were of European ethnicity. Other common ethnic groups included in previous studies were Han Chinese, Hispanics, Israelis, and African Americans with significant ethnic variations in the association between genetic variants and opioid dependence were reported. Most of the studies reviewed were of modest sample size and limited power to detect multiple genetic variants. Few larger studies included Zhang et al.’s study, which examined 1063 European American individuals with 620 cases of substance dependence [12], and Hou et al.’s study of 1030 Han Chinese males with 500 cases of opioid dependence [64]. The results from
