It's an assumption in many contemporary political discussions that the "Just Say No" campaign and, more broadly, Nancy Reagan's campaign against teen drug use were failures. However, the broader trends of Monitoring the Future show a substantial and long-term decline in teen drug use during the 1980s. Media headlines to the contrary, teens today are less likely to use illegal drugs than they were in the early 1980s (this is not to discount the recent explosion of opioid-related deaths, a serious concern but one distinct from teen drug use). During the sustained anti-drug campaigns of the 1980s and early 1990s, teen drug use plummeted.
In 1979, over 54 percent of high school seniors (see Tables 5-1 to 5-4) had used an illicit drug within the past 12 months; by 1992, that had been cut in half, to 27 percent. In 1979, a majority of seniors had used marijuana in the past year, but only 22 percent had in 1992. Similar declines can be seen in the number of high-school seniors who had used illegal drugs in the past month, and, in certain categories, huge declines were seen in the daily use of drugs. For instance, in 1979, almost 10 percent of seniors reported being daily pot users, a number that collapsed to 2 percent by 1991. In many areas, the use of drugs has increased from the nadirs of the early-to-mid-90s (alcohol is an exception to this; it has fallen since the mid-90s). For example, the use of illicit drugs over the past year hovered between the low 30s and high 20s in the early 90s but reached over 40 percent in 2015; the use of illicit drugs other than marijuana has not shown the same increase. By and large, similar trends play out for college students. (An interesting side note is the collapse in cigarette smoking among college students. While the percentage of college students who are daily cigarette smokers did dip in the late 80s and early 90s, it rebounded in the late 90s only to fall through the floor in recent years. Whereas about 18 percent of college students were smokers in 2000, only about 4 percent were in 2015.)
Correlation is, of course, not causation, and there are no doubt a variety of factors that contributed to declining drug use among America's youth. But it seems possible that the sustained White House-led anti-drug campaign played a role in a broader public turn against drug use.