Dhivya Ramalingam, Ph.D.

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Tags:  Cannabis; Cognition; Executive Function; Adolescence

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The problem:  The long-term effects of cannabis on cognitive function are not well-defined. Previous studies have addressed the effect of cannabis on general cognitive function but not on executive function (e.g. the ability to plan, prioritize, and multi-task).

 

Why do this study? With increase in cannabis legalization, it is important to know whether long-term cannabis use is associated with cognitive decline.

 

The study:  The study analyzed cognitive and behavioral data collected from 856 individual twins from 428 families in the Colorado Longitudinal Twin Study. Using this data, phenotypic associations between cannabis initiation, frequency, and use disorder with cognitive abilities were measured at adolescence (Wave 1) or young adult (Wave 2). At Wave 1 (2003–2008), general cognitive ability, executive function (EF, the ability to plan, organize, multi-task or any goal-directed behavior) and substance use were measured at a mean age of ~17. At Wave 2 (2009–2013), cognitive abilities and substance use were measured at a mean age of ~23. Associations between cannabis use and EFs were measured using well-characterized models. In addition, the between- and within-twin associations between cannabis use and intelligence were also measured using multilevel models. The study showed that most associations between cannabis use and cognition were negligible after accounting for other substance use. One twin-specific association that was significant in both identical and fraternal twins was the cannabis frequency at age 17 and EF at age 23. The study showed that an increase in cannabis frequency by 1 day/month at age 17 was associated with a decrease in EFs at age 23.

 

Conclusions:  In general, cannabis use was not associated with a significant decline in cognitive abilities.

 

What does this study add? The analysis of the effect on cannabis on executive function is novel. The study shows that cannabis use is not associated with a significant decrease in cognition or the ability to perform executive functions.

 

Funder:  National Institutes of Health

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Author conflicts:  None

 

Commentary: This study is unique in several ways. Previous twin studies to understand the association between cannabis use and cognition focused on general cognitive abilities and not executive function. The measurement of the effect of cannabis on executive function from adolescence into young adulthood is novel. This study also accounts for substance abuse other than cannabis (e.g. tobacco, alcohol), which is an important factor to consider because it occurs commonly in cannabis users. However, it is important to note that the study utilized data from a mostly Caucasian (92%) population, who were not heavy cannabis users. Therefore, the results might not be broadly applicable to the general population. More importantly, executive function data prior to cannabis use were not available in this study. This makes it difficult to accurately capture the effect of cannabis on decline. Further, factors that are not shared by twins (e.g cannabis exposure and how it is metabolized) may not be accurately captured and hence, can confound the analysis.