Age of onset of marijuana use and executive function.

Abstract

Marijuana (MJ) remains the most widely abused illicit substance in the United States, and in recent years, a decline in perceived risk of MJ use has been accompanied by a simultaneous increase in rates of use among adolescents. In the current study, we hypothesized that chronic MJ smokers would perform cognitive tasks, specifically those that require executive function more poorly than control subjects, and that individuals who started smoking MJ regularly prior to age 16 (early onset) would have more difficulty than those who started after age 16 (late onset). Thirty-four chronic, heavy MJ smokers separated into early and late onset groups and 28 non-MJ smoking controls completed a battery of neurocognitive measures. As hypothesized, MJ smokers performed more poorly than controls on several measures of executive function. Age of onset analyses revealed that these between-group differences were largely attributed to the early onset group, who were also shown to smoke twice as often and nearly three times as much MJ per week relative to the late onset smokers. Age of onset, frequency and magnitude of MJ use were all shown to impact cognitive performance. Findings suggest that earlier MJ onset is related to poorer cognitive function and increased frequency and magnitude of MJ use relative to later MJ onset. Exposure to MJ during a period of neurodevelopmental vulnerability, such as adolescence, may result in altered brain development and enduring neuropsychological changes.

Impact of adolescent marijuana use on intelligence: Results from two longitudinal twin studies

“…Differences between marijuana user groups have appeared in these other cognitive domains (18,23,57,58). Nevertheless, there is no reason to expect such a difference would emerge in the present study.…”

Marijuana Use Predicts Cognitive Performance on Tasks of Executive Function

“…Results indicated that early-onset marijuana smokers performed more poorly on the WCST and Stroop compared with the control group, and the early-onset marijuana group also tended to show impairment relative to the late-onset marijuana group. Correlation analyses have further supported these findings, indicating that earlier age at marijuana onset and increased frequency (smoking episodes/week) and magnitude of marijuana use (grams smoked/week) are all associated with poorer executive functioning (Gruber et al, 2012b).…”

“…Exclusion criteria also included head injury with loss of consciousness, neurological disorders, current or previous use of psychotropic medications, and nonnative English speakers (required for the neurocognitive battery). Although a number of participants had completed other studies, which have previously been published (Gruber et al, 2012b), approximately 35% of the participant pool was newly recruited. Further, regression analyses completed for the current study have not previously been reported.…”

“…Marijuana smokers were also required to abstain from smoking marijuana at least 12 hours before their study visit to ensure that they were not acutely intoxicated at the time of assessment. All participants provided a urine sample on arrival at the labora-tory, and to ensure compliance, marijuana participants were led to believe that researchers could use this sample to detect the last use of marijuana, a method we have successfully used in the past (Gruber & Yurgelun-Todd, 2005;Gruber et al, 2011Gruber et al, , 2012aGruber et al, , 2012bGruber et al, , 2014. Further, all urine samples were screened for illicit and prescription drugs including amphetamines, cocaine, tetrahydrocannabinol (THC), methamphetamine, opioids, phencyclidine (PCP), benzodiazepines, tricyclic antidepressants, barbiturates, methadone, Ecstasy (3,4-methylenedioxymethamphetamine, or MDMA), and oxycodone.…”

“…Further, several investigations have specifically examined the role of age at marijuana onset, with results suggesting that earlier age at marijuana onset is related to impairment on measures of visual scanning (Ehrenreich et al, 1999), verbal IQ (Pope et al, 2003;Solowij et al, 2011), and executive function (Battisti et al, 2010;Fontes et al, 2011;Gruber et al, 2012b). Gruber and colleagues (2012b) found that mari-juana smokers performed more poorly than healthy control subjects on tasks of executive function, including the Wisconsin Card Sorting Test (WCST) and Stroop Color Word Test (Stroop).…”