use illicit drugs, drink alcohol, or smoke do not experience problems, the risk of addiction increases with heavier or more frequent consumption.

In 1995, the Substance Abuse and Mental Health Service Administration's (SAMHSA's) National Household Survey on Drug Abuse estimated that 12.8 million Americans used at least one illicit drug during the past month, constituting 6.1 percent of the population 12 years old or older—a dramatic decrease from 1979 when the number of current illicit drug users was at its highest level of 25 million or 14 percent of the population (SAMHSA, 1996a). Although the estimated number of users has remained at approximately the same level since 1992, rates of drug use show substantial variation by age with the greatest increases of use occurring among young people ages 16–20 (SAMHSA, 1996a) (see Figure 2.1). According to the 1996 National Institute on Drug Abuse's (NIDA) Monitoring the Future Study, 24.6 percent of high school seniors used at least one illicit drug in the past month—a slight increase since 1995 (23.8 percent), reflecting the continued rise in illicit drug use by teenagers since 1992 when the rate was at the lowest percentage of 14.4 (Johnston et al., 1997).

In regard to ethnicity, gender, geography, education, and employment, the rates of current illicit drug use in 1995 varied as follows (SAMHSA, 1996a):

FIGURE 2.1 Past month illicit drug use by age: 1979–1995. SOURCE: SAMHSA (1996a).