"This study of crash risk found a statistically significant increase in unadjusted crash risk for drivers who tested positive for use of illegal drugs (1.21 times), and THC specifically (1.25 times). However, analyses incorporating adjustments for age, gender, ethnicity, and alcohol concentration level did not show a significant increase in levels of crash risk associated with the presence of drugs.

"The public health burden of cannabis use is probably modest compared with that of alcohol, tobacco, and other illicit drugs. A recent Australian study⁹⁶ estimated that cannabis use caused 0·2% of total disease burden in Australia—a country with one of the highest reported rates of cannabis use. Cannabis accounted for 10% of the burden attributable to all illicit drugs (including heroin, cocaine, and amphetamines). It also accounted for around 10% of the proportion of disease burden attributed to alcohol (2·3%), but only 2·5% of that attributable to tobacco (7·8%)."

"Tetrahydrocannabinol is a very safe drug. Laboratory animals (rats, mice, dogs, monkeys) can tolerate doses of up to 1,000 mg/kg (milligrams per kilogram). This would be equivalent to a 70 kg person swallowing 70 grams of the drug—about 5,000 times more than is required to produce a high. Despite the widespread illicit use of cannabis there are very few if any instances of people dying from an overdose.

"Our results indicate a moderate relation between early teen marijuana use and young adult abuse of other illicit substances; however, this association fades from statistical significance with adjustments for stress and life-course variables. Likewise, our findings show that any causal influence of teen marijuana use on other illicit substance use is contingent upon employment status and is short-term, subsiding entirely by the age of 21. In light of these findings, we urge U.S.

"As in previous years, cannabis was the most commonly used drug in 2016/17, with 6.6 per cent of adults aged 16 to 59 having used it in the last year (around 2.2 million people), similar to the 2015/16 survey (6.5%). However, this is statistically significantly lower than a decade ago (8.2% in 2006/07) and the start of measurement in the survey in 1996 (9.4%). The trend from the 2009/10 survey onwards is relatively flat, remaining between six and seven per cent, as illustrated by Figure 1.2 (see Appendix Table 1.02 for detailed figures).

"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.

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)."

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.

"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.