"Synthetic marijuana, so named because it contains synthetic versions of some of the cannabinoids found in marijuana, is a recent and important addition to the smorgasbord of drugs available to young people in the US. These designer chemicals are sprayed onto herbal materials that are then sold in small packets under such brand names as Spice and K-2. They have been readily available as over-the-counter drugs on the Internet and in venues like head shops and gas stations. While many of the most widely used chemicals were scheduled by the Drug Enforcement Administration in March of 2011, making their sale no longer legal, purveyors of these products have skirted the restrictions by making small changes in the chemical composition of the cannabinoids used. Use of these products was first measured in MTF in 2011 in a tripwire question for 12th graders, asking about their frequency of use in the prior 12 months (see Table 2-2). Annual prevalence was found to be 11.4%, making synthetic marijuana the second most widely used class of illicit drug after marijuana that year. In spite of the DEA’s scheduling of the most common ingredients, use among 12th graders remained unchanged in 2012, with 11.3% annual prevalence. Eighth and 10th graders were also asked about use of these drugs in 2012, and their annual prevalence levels were 4.4% and 8.8%, respectively, making synthetic marijuana the second most widely used illicit drug among 10th graders, as well, and the third among 8th graders behind marijuana and inhalants. In 2013 use dropped appreciably in all five populations, including statistically significant drops among 12th graders, college students, and young adults. These declines continued in 2014 with significant drops in prevalence among young adults, college students, 12th and 10th graders (a decline among 8th-grade students was not statistically significant). Efforts by the DEA and various states to make their sale illegal may well have had an impact. In 2015 prevalence continued to decline for 8th, 10th, and 12th grade students, although none of the one-year declines were statistically significant. Among young adults and college students prevalence has leveled, with signs of a possible reversal in course with a slight uptick of .2 points (ns) for young adults and .6 (ns) for college students. There is a relatively low level of perceived risk for trying synthetic marijuana once or twice, despite growing evidence of serious problems resulting from the use of these drugs."
Miech, R. A., Johnston, L. D., O’Malley, P. M., Bachman, J. G., & Schulenberg, J. E. (2016). Monitoring the Future national survey results on drug use, 1975–2015: Volume I, Secondary school students. Ann Arbor: Institute for Social Research, The University of Michigan.