Moderate Cannabis Use Has Adverse Effects on Cognitive Functioning, Study Suggests | Medicine, Neuroscience

Moderate adolescent cannabis use may have adverse effects on cognitive functioning, specifically verbal memory, that cannot be explained by familial factors, according to a study of siblings led by the University of Colorado School of Medicine.

Ellingson et al aimed to examine whether moderate adolescent cannabis use has neurocognitive effects that are unexplained by familial confounds. Image credit: Jui Magicman.

“We wanted to expand our understanding of whether cannabis use is related to lower cognitive functioning,” said study lead author Dr. Jarrod Ellingson, a researcher in the Department of Psychiatry at the University of Colorado School of Medicine and the Institute for Behavioral Genetics at the University of Colorado.

“There’s a large body of evidence that cannabis use is linked to cognitive functioning, but we know that cannabis use is not isolated from other important risk factors (e.g. peer group influence, parental behavior, socioeconomic status).”

“That was the primary motivation behind this study, in which we compared siblings to account for many of these risk factors.”

In the study, Dr. Ellingson and colleagues were able to establish comparisons between siblings and then determine that differential levels of cannabis use were related to poorer cognitive functioning, particularly verbal memory.

A total of 1,192 adolescents from 596 families participated in the study. Participants were primarily male (64%) and racially and ethnically diverse.

Drug use was assessed through clinical interviews and cognitive abilities were analyzed through a battery of neuropsychological tests.

Two waves of data were collected: the first was from participants with an average age of 17 from 2001-2006; the second was collected from 2008-2013, with an average participant age of 24.

“More work needs to be done to determine how cannabis use is related to cognitive functioning and we hope that our study can help inform future study designs,” Dr. Ellingson said.

“These studies are particularly important because cannabis is becoming more potent and more accessible as states legalize its recreational use.”

“Due to changes in the legality of recreational and medical cannabis and widespread access in many states, valid empirical data must be available to inform policy and public health decisions, including how cannabis use may affect the developing brain,” the scientists said.

The results were published in the journal Addiction.


Jarrod M. Ellingson et al. Familial factors may not explain the effect of moderate-to-heavy cannabis use on cognitive functioning in adolescents: a sibling-comparison study. Addiction, published online September 3, 2020; doi: 10.1111/add.15207

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