Cannabis is the second most commonly used drug, with 35.6% of 12th graders using it in the past year (Johnston et al., 2017). Early adolescent cannabis (before age 17) use is strongly correlated with substance use and the abuse of other illicit drug use in youth (Agrawal et al., 2004). While there is still some degree of debate (National Academies of Sciences E. and Medicine, 2017), converging data reflect that at least weekly cannabis use during adolescence has been associated with neurocognitive abnormalities, including abnormal brain morphometry and function, lower IQ, and poorer sustained attention, verbal memory, and executive function, especially in those with an early age of cannabis use onset see (Lisdahl et al., 2013; Batalla et al., 2013; Lisdahl et al., 2014; Meruelo et al., 2017; Jacobus and Tapert, 2014 for reviews). It is notable that there have been challenges to this research in terms of the wide array of metrics, lack of measurement of potency and content of cannabinoids [e.g., tetrahydrocannabinol (THC), cannabidiol (CBD)], lack of control of polysubstance use (especially alcohol and nicotine), and the majority are cross-sectional studies, making it difficult to resolve the temporal sequencing of substance exposure and neurocognitive deficits.
