An estimated 2.3 million Americans used marijuana for the first time in 1994. The number has been increasing since 1991, after a long-term decrease that had been occurring since 1975. It is interesting to note that the decrease in prevalence of marijuana use that occurred in the 1980s did not begin to occur until several years after the peak in incidence estimates. This suggests that unless there are changes in the factors that influence drug use behaviors, we should not expect decreases in prevalence to occur soon, since incidence was still rising in 1994. The rising incidence seems to be fueled largely by the increasing rate of new use among youths age 12-17 years (from 38 per 1,000 person years in 1991 to 74 per 1,000 person years in 1994). This is in contrast with the epidemic of the late 1960s and early 1970s, which involved increases among youths and young adults (Figure 10).