Several comprehensive reviews describe the role of the endogenous opioid family of genes in addiction and treatment responses (e.g. Kreek et al. 2005; Kreek et al. 2009; LaForge et al. 2000; Yuferov et al. 2010). In this review we will focus on the genetics of the opioid system that is relevant to addiction to opioids, cocaine, alcohol and methamphetamines, with particular emphasis given to genetic association studies and functional studies. Cannabis or tobacco dependence will not be discussed. We will also discuss the genetics of the opioid system in relation to specific addiction treatments (methadone, buprenorphine, naltrexone and nalmefene), as well as stress responsivity and the hypothalamic-pituitary-adrenal (HPA) axis.
