Proportion of Students Using Any Drug Changes Slowly
"Overall, these data reveal that, while use of individual drugs (other than marijuana) may fluctuate widely, the proportion using any of them is much more stable. In other words, the proportion of students prone to using such drugs and willing to cross the normative barriers to such use changes more gradually. The usage rate for each individual drug, on the other hand, reflects many more rapidly changing determinants specific to that drug: how widely its psychoactive potential is recognized, how favorable the reports of its supposed benefits are, how risky its use is seen to be, how acceptable it is in the peer group, how accessible it is, and so on."
Johnston, L. D., O’Malley, P. M., Bachman, J. G., & Schulenberg, J. E. (2013). Monitoring the Future national results on adolescent drug use: Overview of key findings, 2012. Ann Arbor: Institute for Social Research, The University of Michigan, p. 10.