Data for the study were obtained from the National Household Surveys on Drug Abuse, which is a time series of nine surveys that spanned 18 years, from 1971 to 1988. Trends from the data show a clear break and reversal of drug usage in the younger population in 1979. The same break in the upward trend is apparent for older drug users, but the decline does not appear until the mid-1980's. Simulation of the model that reproduced rising enforcement expenditures failed to show any concomitant reversal in trends in users. Various considerations suggest that the primary source of the reversal in use trends must lie in the sphere of informal social control. Opinion survey data suggest that there have been some dramatic shifts in Americans' willingness to legitimate drug use. Education may have been a factor in this shift, but there must have been exogenous forces, such as the AIDS scare of the early 1980's, to have triggered the abrupt change. 8 figures, 2 tables, and 11 references