Long Term Trends In Prevalence of Marijuana Use Among Youth

"Marijuana use declined in the early 2000s, but subsequently rebounded before leveling in the past couple of years. In 2014 the percentage of youth who used marijuana in the past year among students in 12th, 10th, and 8th grade was 35.1%, 27.3%, and 11.7%, respectively.

"It is important to note that 8th grade students were the first to show the two major shifts in marijuana prevalence — an increase at the start of the 1990s and a decrease by the end of the 1990s. As mentioned above, this suggests that 8th graders may be the most immediately responsive to changing influences in the larger social environment. The lag in the decline in the later grades likely reflects some cohort effects (i.e., lingering effects of changes in use that occurred when the students were in lower grades).

"Levels of annual marijuana use today are considerably lower than the historic highs observed in the late 1970s, when more than half of U.S. 12th graders had used marijuana in the past year. This high point marked the pinnacle of a rise in marijuana use from relatively negligible levels before the 1960s.²

"Important changes in young people’s attitudes and beliefs about marijuana use have occurred over the study period, and these changes can account for much of the long-term decline in use, as well as the increase in use during the 1990s drug relapse. Chapter 8 contains a more thorough discussion of this issue.

"• Figure 5-4a and Table 5-5d provide trends in daily marijuana use. These trends depart somewhat from the typical pattern seen for drug use because, among 12th graders, today’s level of use is actually higher than it was at the end of the 1990s relapse period. Although daily use of marijuana declined somewhat in 2014 as compared to the previous year, the average level since 2010 (i.e., 2011–2014 combined) is the highest recorded in the past two decades. (See Chapter 10 for additional information on the cumulative amount of daily marijuana use among 12th graders. It shows that the proportion using marijuana daily for a month or more at any time in the past is considerably higher than the proportion reporting daily marijuana use during just the past month.) The overall trends follow a similar pattern in 12th, 10th, and 8th grade, and in 2014 prevalence levels of daily marijuana use were 5.8%, 3.4%, and 1.0%, respectively. About one in every 17 twelfth-grade high school students in 2014 was a daily or near-daily marijuana user.

"Still, the percentage of youth using marijuana on a daily basis today is substantially lower than its peak in the late 1970s, when it reached a high of 10.7% among 12th grade students. As we will discuss in Chapter 8, we think much of the decline from this peak is attributable to a very substantial increase in teens’ concerns about possible adverse effects from regular use and to a growing perception that peers disapproved of marijuana use, particularly regular use. The recent surge in daily marijuana use since 2009 among 12th-grade students tracks with concurrent, decreasing levels of perceived harmfulness and disapproval of regular marijuana use.

"• In 2014 marijuana use showed a one-year, slight decline in lifetime, annual, thirty-day, and daily use in all three grades. This finding is unexpected in light of the positive publicity marijuana has received in recent years prior to the data collection in 2014, with several states allowing medical marijuana use and two states (Colorado and Washington) legalizing recreational use for adults. Further, perceived risk of marijuana use among adolescents has declined in recent years (discussed in more detail in Chapter 8), which also supports an expectation for an increase in marijuana use this year. The study results point to the need for further qualitative and quantitative research to analyze why marijuana use has not increased in the last two or three years as expected."