"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.

Estimated Prevalence of Cannabis Dependence: "Some 4.3 percent of Americans have been dependent on marijuana, as defined in the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision (DSM-IV-TR; American Psychiatric Association, 2000), at some time in their lives. Marijuana produces dependence less readily than most other illicit drugs. Some 9 percent of those who try marijuana develop dependence compared to, for example, 15 percent of people who try cocaine and 24 percent of those who try heroin. However, because so many people use marijuana, cannabis dependence is twice as prevalent as dependence on any other illicit psychoactive substance (cocaine, 1.8 percent; heroin, 0.7 percent; Anthony and Helzer, 1991; Anthony, Warner, and Kessler, 1994)."

"Marijuana, the most widely used of the illicit drugs, did not show any significant change in annual prevalence this year in any of the three grades, nor in the three grades combined. After rising for several years, the annual prevalence of marijuana has more or less leveled out since about 2010.

"• Marijuana is by far the most widely used illicit drug. Nearly half of all 12th graders (45%), nearly one third of 10th graders (31%), and over one in seven 8th graders (14%) reported some marijuana use in their lifetime. Among 12th graders, 37% reported some use in the past year, and 23% reported some use in the past month. Among 10th graders, the corresponding percentages were 26% and 16%, respectively, and among 8th grade students, 10% and 5.5%.

Prevalence of Cannabis Use Among Youth in Australia: "Cannabis was the illicit substance most commonly used by secondary school students and prevalence was highest in the older age groups. Sixteen per cent of secondary students surveyed indicated they had used cannabis at some time in their lives with seven per cent using it in the past month and four per cent using it in the past week.
"In all recency periods the proportion of students using cannabis increased significantly with age (p<0.01).

According to the Substance Abuse and Mental Health Service's Treatment Episode Data Set, in 2015 in the US there were 213,001 admissions to treatment with marijuana reported as the primary substance of abuse out of the total 1,537,025 admissions to treatment in the US for those aged 12 and older for all substances that year. This is the lowest number of marijuana admissions and total treatment admissions in at least a decade: marijuana admissions peaked in 2009 at 373,338, and total admissions peaked in 2008 at 2,074,974.

"In 2018, an estimated 164.8 million people aged 12 or older used a substance (i.e., tobacco, alcohol, or an illicit drug) in the past month (Figure 1). This number of current substance users corresponds to 60.2 percent of the population. About 2 out of 5 people aged 12 or older (108.9 million, or 39.8 percent) did not use substances in the past month. The 164.8 million current substance users in 2018 include 139.8 million people who drank alcohol, 58.8 million people who used a tobacco product, and 31.9 million people who used an illicit drug (2018 DT 7.3).

"Annual marijuana prevalence peaked among 12th graders in 1979 at 51%, following a rise that began during the 1960s. Then use declined fairly steadily for 13 years, bottoming at 22% in 1992—a decline of more than half. The 1990s, however, saw a resurgence of use. After a considerable increase (one that actually began among 8th graders a year earlier than among 10th and 12th graders), annual prevalence rates peaked in 1996 at 8th grade and in 1997 at 10th and 12th grades. After these peak years, use declined among all three grades through 2007 or 2008.

"The teen brain is a work in progress, making it more vulnerable than the mature brain to the physical effects of drugs. The potential for developing substance abuse and dependence is substantially greater when an individual’s first exposure to alcohol, nicotine and illicit drugs occurs during adolescence than in adulthood."

"Nationwide, 35.6% of students had used marijuana (also called grass, pot, or weed) one or more times during their life (Supplementary Table 106). The prevalence of having ever used marijuana was higher among black (42.8%) and Hispanic (42.4%) than white (32.0%) students, higher among black female (44.9%) and Hispanic female (42.7%) than white female (32.1%) students, and higher among black male (40.5%) and Hispanic male (42.1%) than white male (31.7%) students.