Total US
According to the National Survey on Drug Use and Health (NSDUH), in 2008-2009, an estimated 13.37% of young people in the US aged 12 through 17 had used marijuana in the past year, falling to 12.29% in 2015-2016. The NSDUH also estimates that, in 2008-2009, an estimated 7.03% of young people in the US aged 12 through 17 had used marijuana in the past month, dropping to 6.75% in 2015-2016.

"Hepatitis C is associated with more deaths in the United States than 60 other infectious diseases reported to CDC combined. Despite curative hepatitis C virus (HCV) therapies and known preventive measures to interrupt transmission, new HCV infections have increased in recent years (1,2). Injection drug use is the primary risk factor for new HCV infections (2). One potential strategy to decrease the prevalence of HCV is to create and strengthen public health laws and policies aimed specifically at reducing transmission risks among persons who inject drugs."

"In 2016, the estimate of about 1.9 million people aged 12 or older who were current users of cocaine (Figure 15) included about 432,000 current users of crack. The numbers correspond to about 0.7 percent of the population aged 12 or older who were current users of cocaine (Figure 22) and 0.2 percent who were current users of crack (Table A.7B in Appendix A). The 2016 estimate for current cocaine use was similar to the estimates in most years between 2007 and 2015, but it was lower than the estimates in 2002 to 2006.

"In these initial investigations, we found no evidence that I-502 enactment, on the whole, affected cannabis abuse treatment admissions. Further, within Washington State, we found no evidence that the amount of legal cannabis sales affected cannabis abuse treatment admissions.

"The bulk of outcome analyses in this report used the within-state approach to focus on identifying effects of the amount of legal cannabis sales. We found no evidence that the amount of legal cannabis sales affected youth substance use or attitudes about cannabis or drug-related criminal convictions.

"Illicit drug use disorder is defined as meeting DSM-IV criteria for either dependence or abuse for one or more of the following illicit drugs: marijuana, cocaine, heroin, hallucinogens, inhalants, methamphetamine, or prescription psychotherapeutic drugs that were misused (i.e., pain relievers, tranquilizers, stimulants, and sedatives). There are seven possible dependence criteria for specific illicit drugs:
"1. spent a lot of time engaging in activities related to use of the drug,
"2. used the drug in greater quantities or for a longer time than intended,

Illegal Drug Use and Marijuana Use in Lifetime, Past Year, and Past Month among Persons Aged 12 and Older in the US by Age, Gender, and Race/Ethnicity, 2015 and 2016

"Cigarette smoking has been shown in other studies to act as a 'gateway' to cannabis use and further risk taking behaviours. This study aims to establish the prevalence of cigarette smoking and cannabis use in Irish teenagers, to quantify the strength and significance of the association of cigarette smoking and cannabis use and other high risk behaviours and to examine whether the above associations are independent of social networking (O'Cathail, et al. 2011).

"By combining the data from 2012 and 2013, we can obtain more precise estimates of prevalence levels for cannabis use and differences between subgroups. The estimated LTP [lifetime prevalence], LYP [last year prevalence] and LMP [last month prevalence] rates among all adults (aged 16–64) were 21.3 per cent, 4.3 per cent and 1.6 per cent, respectively. Among young adults (aged 16–34), the corresponding LTP, LYP and LMP estimates are 30.2 per cent, 10 per cent and 3.4 per cent.

"• 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%.

"Comparisons with the previous four sweeps of the SCJS [Scottish Crime and Justice Survey] help to put these findings in context and reveals that the percentage of adults reporting using one or more illicit drugs has been declining. Table 2.1 and Figure 2.1 show this decline in the number of adults reporting illicit drug use for all three time periods used in the survey between the SCJS 2008/09 and the SCJS 2014/1510. The decline was significant comparing drug use reported in the 2008/09 survey with that reported in 2014/15.