"Generally, between 1995 and 2011, there was an increase in the lifetime prevalence of illicit drug use, most of which occurred between 1995 and 1999. Since 2011, the prevalence has started to decrease slowly. The lifetime prevalence of illicit drug use among boys and girls follows a parallel trend, with the rate among girls being about 5-6 percentage points lower than that among boys (Figure 21).

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 2018, an estimated 5.5 million people aged 12 or older were past year users of cocaine (Figure 10), including about 757,000 users of crack. Stated another way, about 2.0 percent of the population in 2018 used cocaine (Figure 13), and 0.3 percent used crack (2018 DT 7.2).

"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., stimulants, tranquilizers or sedatives, and pain relievers).⁴⁴ There are seven possible dependence criteria for specific illicit drugs:

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.

"• Figure 5-4a and Table 5-5d provide trends in daily marijuana use, defined as using marijuana on 20 or more occasions in the prior 30 days. Among 12th grade students, the 2019 level of 6.4% is the highest level recorded by the survey since 2013. About one in every 16 twelfth grade students in 2019 was a daily or near-daily marijuana user. Daily marijuana use significantly increased in 8th and 10th grade in 2019, to 1.3% and 4.8%, respectively.