Despite data indicating high rates of prescription drug abuse, a major limitation of the existing research is that the terms misuse, abuse, dependence, and addiction are used in idiosyncratic ways. To make the nomenclature consistent, a minimum guideline would be for each researcher and author to specify their definitions clearly. In this chapter, abuse is defined as any intentional use of opioids outside of a physician's prescription for a bona fide medical condition, excluding accidental misuse. Note that our use of the term abuse is distinct from the abuse diagnosis specified in DSM-IV-TR (American Psychiatric Association 2000). However, addiction in this chapter is synonymous with the standard DSM-IV-TR diagnosis of dependence, which is a psychiatric syndrome defined as including compulsive use, impaired control, tolerance, withdrawal, and continued use despite physical and psychological problems caused or exacerbated by use (American Psychiatric Association 2000).