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Aberrant patterns of substance use have long been recognized
Aberrant patterns of substance use have long been recognized as a significant clinical and public health problem. Among adults, substance use problems are quite common (). Recent surveys indicate that 7.8% of U.S. adults over the age of 18 had one or more substance use disorders in the past year (), largely driven by alcohol use problems. It is broadly perceived that substance use, as a privileged behavior, can readily escalate out of one\'s control in the absence of appropriate behavioral boundaries. Indeed, a large percentage of the world gsk-3 has struggled with substance use disorders at some point within their lifetime (). Data from the study (), funded by the U.S. National Institute on Drug Abuse, consistently indicate that marijuana is the most commonly used illicit substance, a pattern that reflects worldwide trends (). Within the United States, substances such as alcohol and nicotine can be legally purchased and ingested in public places at the age of 21; in most of Europe and the UK, the legal drinking age is 18. The legalization of recreational marijuana use is much more recent, and within the 
United States, highly controversial. At the time of this writing, four States (Oregon, Washington, Colorado, Alaska) and the District of Columbia have legalized recreational marijuana use and 23 States plus the District of Columbia have legalized use for medical purposes (). Importantly, however, legalization is not yet recognized at the federal level, subsequently resulting in some degree of conflict around the “acceptability” of this substance use behavior. More importantly, in the interim, it is feared that increasing access to this drug for many individuals, including adolescents, may represent an unforeseen consequence of legalized medical use (). In other Western countries, such as the United Kingdom and European Union, the age at which one can legally use alcohol, nicotine, and marijuana varies. In the Netherlands, for example, cannabis can be legally purchased only in designated coffeeshops whereas alcohol can be legally used at any age but can be purchased at age 18.
Within the scientific community, the manner in which these standards that regulate access are adopted and enforced inspires debate, because while it is recognized that experimentation with such substances is highly typical for many adolescents and often time-limited (naturally remitting by mid-adulthood, concurrent with youths’ adoption of more “adult” responsibilities; ), earlier first-time users of alcohol and marijuana show elevated risks of developing substance use disorders in adulthood (). Moreover, recent reviews have shown that even modest levels of alcohol use can be linked to differences in neural structure and function during adolescence (e.g., ), and similar trends are evident for marijuana (). Moreover, the use of alcohol and marijuana in large quantities has been associated with cognitive problems, particularly in the areas of learning and memory, attention, and executive function (). At least one longitudinal study suggests that chronic marijuana use, particularly when use begins in adolescence, leads to later declines in general intellectual function (), and similar findings are reported in relation to more specific domains of cognition (). Negative outcomes are particularly salient in the contexts of earlier use onset (