entified, although there is no inevitability about the pattern of escalation:
Beer and wine are the initial drugs used by teens.
Tobacco and hard liquor are used after introduction to beer and wine.
Marijuana is tried, often together with alcohol.
Illicit drugs such as psychedelics or heroin may be used after, or in conjunction with, marijuana (Kleber, 1999)
Kleber explains that the normal course of maturation causes those who might use illicit drugs while adolescents to stop doing so in their twenties, many never having reached stage 3 or 4. However, the fact that evolving social experience may have an impact on drug-use patterns is relevant to the origins and causes of drug use by adolescents. In this regard, Chard, Lilford, and Gardiner (1999, p. 486) make the point that "social variables remain the most important determinants of health."
Social/environmental/behavioral causes of drug use have been identified in the literature. Peer pressure is implicated in use of tobacco, marijuana, and alcohol. Parental example has also been cited in the case of teen use of alcohol. In the case of illicit-drug use by teens (e.g., cocaine, heroin), the causes appear to be more complex. While peer pressure or exposure to peers may be a factor, there may also be a more general dysfunctional pattern at work--bad parent-child relationships, parental drug abuse, domestic violence, and/or psychological distress of some kind (Kleber, 1995; Johnson, 1999).
Drug abuse may also have a physical origin, in the shape of drug use. But this is a complex point. Drugs provide a brain-chemistry rush that reinforces the experience of benefit associated with using them. Addictive drugs "stimulate the release of dopamine in the nucleus accumbens [section of the brain], a structure that plays an important role in reinforcement" (Carlson, 1999, p. 498). Now the physiological impact of addictive drugs may be progressive and cumulative, pointing toward...