Opioid addiction has reached epidemic levels around the world, with over-prescription of opioid pain relievers being an often-cited reason for the epidemic in the USA. This project looks at opioid addiction from three perspectives: a review of literature dealing with the neural pathways involved in opioid use and addiction; the underlying genetic differences that can increase the risk of opioid use disorder; and an overview of the public health aspects of the epidemic. The paper will conclude with a review of current and new treatments based upon a growing neurobiological and molecular understanding of opioid use disorder.