Initiation of Moderately Frequent Cannabis use in Adolescence and Young Adulthood is Associated with Declines in Verbal Learning and Memory: A Longitudinal Comparison of Pre- versus Post-Initiation Cognitive Performance

Abstract

Objective:Cannabis use is associated with relative cognitive weaknesses as observed by cross-sectional as well as longitudinal research. Longitudinal studies, controlling for relevant confounds, are necessary to differentiate premorbid from post-initiation contributions to these effects.Methods:We followed a sample of adolescents and young adults across ten years. Participants provided neurocognitive data and substance use information at two-year intervals. Participants who initiated cannabis and/or alcohol use were identified (n = 86) and split into alcohol-only initiators (n = 39) and infrequent (n = 29) and moderately frequent (n = 18) cannabis initiators. Participants completed the Rey Auditory Verbal Learning Task (RAVLT) and the Iowa Gambling Task (IGT). Group differences before and after substance use initiation and the extent to which alcohol, nicotine, and cannabis use frequencies contributed to cognitive functions over time were examined.Results:After controlling for parental education, RAVLT new learning was worse in moderately frequent cannabis users prior to use initiation. RAVLT total learning and delayed recall showed significant declines from pre- to post-initiation in moderately frequent cannabis users. Regression analyses confirmed that frequencies of cannabis, but not alcohol, use contributed to post-initiation variations. Nicotine use showed an independent negative association with delayed memory. Findings for the IGT were not significant.Conclusions:Verbal learning and memory may be disrupted following the initiation of moderately frequent cannabis use while decreased new learning may represent a premorbid liability. Our use of a control group of alcohol-only users adds interpretive clarity to the findings and suggests that future studies should carefully control for comorbid substance use.

Prospective, longitudinal study to isolate the impacts of marijuana use on neurocognitive functioning in adolescents

“…Researchers interested in a variety of problems extending from the use of marijuana have focused extensively on this period of development when adolescents are susceptible to use and may eventually misuse substances due to both environmental influences and neurodevelopmental vulnerability ( 2 ). Although most previous studies have not been able to isolate the neurocognitive consequences of marijuana due to the lack of a substance-naïve baseline, there is a growing number of investigations that will shed light on this outstanding question ( 69 ). At present, however, there are no longitudinal studies in the extant literature that employ growth models to ascertain both short-term and long-term effects of marijuana.…”

Alcohol and cannabis co‐use and longitudinal gray matter volumetric changes in early and late adolescence

“…Exceptions include prior work showing that the onset and frequency of cannabis use in early adolescence and young adulthood were associated with declining neurocognitive functions. 23,32 Moreover, adolescent cannabis use frequency increased significantly over five biannual assessments along with impairment in motivation. 33 Additional work is necessary to understand the longitudinal impact of cannabis use, alcohol use, and co-use of these substances on the brain.…”

“…Fewer longitudinal studies exist examining the impact of cannabis use on the brain. Exceptions include prior work showing that the onset and frequency of cannabis use in early adolescence and young adulthood were associated with declining neurocognitive functions 23,32 . Moreover, adolescent cannabis use frequency increased significantly over five biannual assessments along with impairment in motivation 33 .…”