Abstract
Opioid addiction is a major medical and social problem worldwide. Chronic use of opioids causes long-term adaptations in the nervous system. These neuroadaptations underlie behavioral manifestations of opioid dependence and are thought to be important in the compulsive nature of drug taking, drug craving, and vulnerability to relapse during abstinence. In this article, we discuss the consequences of opioid use in a chronological manner from first drug encounters to addiction and relapse.