Substance use during adolescence
     Despite an intense and costly war on drugs, substance use among adolescents in the United States has generally risen during the past decade after declining in the late 1980’s (please see the chart below). Use of tobacco, marijuana, cocaine and heroin all increased between 1991 and 1999 (Kann et al., 2000; Johnston et al., 2001). In 2000, heroin use was the highest it had been in 25 years, and use of ecstasy nearly doubled from 6% in 1996 to 11% (Johnston et al., 2001). To make matters worse, the purity of both cocaine and heroin has risen considerably in the past decade while the prices of these and other drugs have fallen (ONDCP, 2001). Increases in use and changes in purity have contributed to a sharp rise in emergency room visits related to drug use (DAWN, 2001).

     The proportion of high school students consuming alcohol, as well as the rate of heavy drinking, remained relatively stable during the past 10 years (Kann et al., 2000; Johnston et al., 2001). Current estimates suggest that roughly 50% of high school seniors consume alcohol at least once per month, while 17% regularly smoke cigarettes and nearly 50% have smoked marijuana (Kann et al., 2000; Johnston et al., 2001). By the time an adolescent reaches 8th grade, nearly 1/2 have had at least one drink, and 1/5 have been "drunk" (NIAAA, 2003). Alcohol use continues to kill more adolescents than all illegal drugs combined (NIAAA, 2003). As the use of many drugs has increased during the past decade, the perceived risk associated with such use has decreased. From 1991 to 2000, the percentage of 12th graders who considered regular use of marijuana to pose a “great risk of harm” dropped from 79% to 58%, while those perceiving great risk associated with drinking four or five drinks per day, nearly everyday, dropped from 70% to 60% (Johnston et al., 2001). Similar decreases in the perception of risk were observed for use of powder and crack cocaine, crystal methamphetamine, and LSD (Johnston et al., 2001).
     At the same time, both attitudes toward drug use and perceived ease of access to drugs also changed. Disapproval of regular marijuana use dropped from 90% in 1991 to 80% in 2000, and disapproval of regular cocaine, LSD, heroin, tobacco, and heavy alcohol use either decreased slightly or remained relatively stable during this time period (Johnston et al., 2001). In addition, the data suggest that it is easier now for high school students to get many drugs, including marijuana, LSD, ecstasy, and heroin, than it was a decade ago (Johnston et al., 2001).
     Given these trends, it is not surprising that the number of adolescents in drug and alcohol treatment programs has increased dramatically in recent years. Between 1993 and 1998, the number of adolescents entering treatment rose more than 45%, from roughly 95,000 to 138,000 (SAMSHA, 2000). Most of the growth in the patient population was due to an increase in admissions for marijuana abuse/dependence. Enrollments in which marijuana was the primary drug of abuse increased from 32% in 1993 to 57% in 1998. During this same period, enrollments in which alcohol was the primary drug of abuse dropped significantly, from roughly 50% to 25% (SAMSHA, 2000).
     Under any circumstances, increases in the abusive use of drugs among adolescence should be troubling. Findings from recent neurobiological studies make these surges in use a serious cause for concern. As summarized above, it has recently become clear that, in contrast to previous assumptions, there is a tremendous amount of brain development taking place during adolescence. We will now discuss evidence that 1) alcohol, and perhaps other drugs, affect both behavior and brain function differently in adolescents than adults, and 2) adolescents may be more vulnerable to the long-term effects of alcohol abuse.
     Before discussing these recent findings, it is important to note that this research is still in its infancy. Much of what is known right now regarding differences in the impact of substances on behavior and brain function in adolescents and adults pertains to alcohol use. As research proceeds, much more will be learned regarding differences in the effects of other drugs. In addition, for a variety of fairly obvious reasons, most of the research on this topic has been conducted using non-human animal models. It has yet to be determined whether all of the differences observed in other animals map onto the human condition, though we certainly expect this to be the case.