Course and Natural History
The natural history of substance dependence characteristically follows the course of a chronic relapsing disorder, although a large number of individuals who experiment with potentially abusable drugs in adolescence do not go on to acquire dependence. The initial phase of the natural history of experimenting with drugs has been well described in studies by Kandel (1975), who has used the concept of gateway drug use and its evolution into more serious drug dependence during adolescence and the early twen-ties. The later phases of dependence are characterized in the 20-to 30-year follow-up studies of individuals with alcoholism and those with opioid addiction by Vaillant (1988, 1983) and Laub and Vaillant (2000). He has documented the natural history after age 20 years in delinquent boys, which is most closely synonymous with having lifetime conduct disorder using DSM-IV-TR criteria, and found high mortality rates by age 40 years in those delin-quent boys who later become substance users. In his most recent studies following 475 delinquent boys and 456 matched nonde-linquent comparison boys from age 14 years until age 65 years he found that 13% of the delinquent and only 6% (N 5 28) of the nondelinquent subjects died unnatural deaths. These deaths were significantly associated with abuse of alcohol during adulthood and childhood delinquency, and these two factors completely ac-counted for the other associations of adult crime, dysfunctional home environment and poor education with the increased mortal-ity. Thus, abusing substances may have a critical impact on later health, but having a conduct disorder as a child increases this risk, perhaps due to related behaviors such as unwillingness to seek out appropriate health care. Clearly, these studies open more questions about the interaction of substance abuse and childhood behaviors that may not include substance abuse.
Population surveys, such as the high school senior surveys and National Institute on Drug Abuse household survey (Wallace et al., 1999), have provided repeated cross-sectional data on changing trends in substance use and its associated problems. These surveys have increasingly recognized cultural differences in the course of drug use. Individuals with substance dependence also have been followed up in a variety of longitudinal treatment studies such as the Drug Abuse Treatment Outcome Studies (DATOS) (Flynn et al., 1999; Simpson et al., 1999). These sur-veys and treatment follow-up studies provide indications of how the natural history of substance abuse changes over the course of several decades. In contrast to most medical disorders, sub-stance abuse and dependence differs because the substances of abuse change over time as epidemics come and go and as new drugs, such as the “designer drugs”, are developed. The natural history of abuse and dependence on these new substances can be unique, with patterns of sustained low-level use, such as with methylenedioxymethamphetamine (Ectasy), or associated social phenomena, such as parkinsonism in abusers of fentanyl-related designer drugs. Thus, the natural history of substance abuse and dependence is determined by the type of substance used and, for polysubstance dependence, can be complicated by changing sec-ular trends and epidemics lasting from months to decades.