"Several meta-analyses of multiple studies found that the risk of being involved in a crash significantly increased after marijuana use13 -- in a few cases, the risk doubled or more than doubled.14-16 However, a large case-control study conducted by the National Highway Traffic Safety Administration found no significant increased crash risk attributable to cannabis after controlling for drivers’ age, gender, race, and presence of alcohol.17"
Eight states have legalized adult (aged 21 and older) personal use of marijuana and legally regulate the production, distribution, and sale of marijuana: Alaska, California, Colorado, Maine, Massachusetts, Nevada, Oregon, and Washington state. Additionally, the state of Vermont and the District of Columbia have legalized limited personal possession and cultivation of marijuana by adults aged 21 and older.
Effect of Cannabis Use by Adolescents on Cognition and IQ and the Potential Influence of Tobacco: "Compared with those in our sample who had never tried cannabis, teenagers who had used cannabis at least 50 times were 17 times more likely (84% vs. 5%) to have smoked cigarettes more than 20 times in their lifetime. Accounting for group differences in cigarette smoking dramatically attenuated the associations between cannabis use and both IQ and educational performance.
Effect of Marijuana Use by Adolescents on Cognition and IQ: "In summary, the notion that cannabis use itself is causally related to lower IQ and poorer educational performance was not supported in this large teenage sample. However, this study indeed has limitations, in particular the young age of outcome assessment.
Effect of Marijuana Use by Adolescents on Cognition and IQ Development
Cannabis and Mortality: "In summary, this study showed little, if any, effect of marijuana use on non-AIDS mortality in men and on total mortality in women. The increased risk of AIDS mortality in male marijuana users probably did not reflect a causal relationship, but most likely represented uncontrolled confounding by male homosexual behavior. The risk of mortality associated with marijuana use was lower than that associated with tobacco cigarette smoking."
Is Marijuana Addictive? The best scientific data available indicate that marijuana is less potentially addictive than many other substances in common use. This should not be construed as meaning that marijuana has no potential for dependence or that it is entirely safe.
"Although the mean annual opioid analgesic overdose mortality rate was lower in states with medical cannabis laws compared with states without such laws, the findings of our secondary analyses deserve further consideration. State-specific characteristics, such as trends in attitudes or health behaviors, may explain variation in medical cannabis laws and opioid analgesic overdose mortality, and we found some evidence that differences in these characteristics contributed to our findings.
The NY Times On Marijuana And Emergency Department Admissions
The Times misses part of the story when they write:
"Marijuana was found -- alone or in combination with other drugs -- in more than 455,000 patients visiting emergency rooms in 2011."