In this article we reviewed the genetics of the endogenous opioid system genes, including association studies, which identified variants that may contribute to the vulnerability to develop specific drug addiction or common drug liability. We also discussed the genetics of the HPA axis and the pharmacogenetics of current treatment for addiction. Association studies in complex disorders such as addiction are challenging. Nevertheless, there is growing evidence for association and/or functionality of several SNPs in the opioid system genes that may have implications for understanding the addictive diseases and for improvements in treatment strategies and personalized medicine. More work is clearly needed to verify the role of variants suggested to be associated with addiction in small studies and for better understanding of their role in different populations.
