"MTF first addressed the use of synthetic marijuana in its 2011 survey by asking 12th graders about their use in the prior 12 months (which would have covered a considerable period of time prior to the drugs being scheduled by the DEA). Annual prevalence was found to be 11.4%, making synthetic marijuana the second most widely used class of illicit drug after marijuana itself among 12th graders at that time. Despite the DEA’s intervention, use among 12th graders remained unchanged in 2012 at 11.3%, which suggests either that compliance with the new scheduling had been limited or that producers of these products succeeded in continuing to change their chemical formulae to avoid using the ingredients that had been scheduled, or both. In 2012, for the first time, 8th and 10th graders were asked about their use of synthetic marijuana; their annual prevalence rates also were high at 4.4% and 8.8%, respectively. Use in all three grades dropped in 2013, with a sharp and significant decline among 12th graders, as well as a significant declines for both 10th and 12th graders in 2014. Since those initial measures, annual prevalence has declined appreciably and in 2020 was down to 1.6%, 2.5%, and 2.4% for the three grades."
Johnston, L. D., Miech, R. A., O’Malley, P. M., Bachman, J. G., Schulenberg, J. E., & Patrick, M. E. (2021). Monitoring the Future national survey results on drug use 1975-2020: Overview, key findings on adolescent drug use. Ann Arbor: Institute for Social Research, University of Michigan.