"Marijuana has been the most consistently available illicit drug and has shown only small variations over the years (see Figure 9-5a). What is most noteworthy is how little change has occurred in the proportion of 12th graders who say that marijuana is fairly or very easy to get. By this measure, marijuana has been readily available to the great majority of American 12th graders (from 80% to 90%) since 1975.
"While variability has been small over the course of the survey, perceived availability of marijuana is at or near historic lows in each grade. In 2019 in 8th grade it was 35% (tied with 2016, 2017, and 2018 for a historic low), in 10th grade it was 66% (the third lowest level recorded by the survey, just above the 2016 low), and in 12th grade it was at 78% (the lowest level ever recorded by the survey). This decline in perceived availability is somewhat counter-intuitive and unexpected, given the widespread adoption of medical marijuana laws and recent legalizing of recreational marijuana use for adults in several states."
Miech, R. A., Johnston, L. D., O’Malley, P. M., Bachman, J. G., Schulenberg, J. E., & Patrick, M. E. (2020). Monitoring the Future national survey results on drug use, 1975–2019: Volume I, Secondary school students. Ann Arbor: Institute for Social Research, The University of Michigan.