a most widely abused licit drug is alcohol, targeting several receptors and ion channels in the brain and representing a major health problem (Hyman, 2008). It is now well established that the endogenous opioid system plays an important role in acute and chronic effects of all these drugs. The exact nature of opioid receptor or peptide involved has been clarified over the years, largely owing to genetic approaches, and this large set of data is overviewed here.
