Cannabis use during adolescence is associated with impaired brain development, according to a new study published in JAMA Psychiatry. The new research represents the largest longitudinal neuroimaging study of cannabis use to date.

Although some studies have found evidence that adolescents who use cannabis tend to have reduced cortical thickness in the frontal regions of the brain, the cross-sectional nature of previous research has not revealed whether these differences in the structure of the brain. brain are a consequence of the drug itself.

“Despite growing trends in cannabis legalization, there have been surprisingly few longitudinal imaging studies on this topic. Most imaging studies of cannabis use have been relatively small in size and cross-sectional in nature, ”said study author Matthew D. Albaugh, registered clinical psychologist and assistant professor of psychiatry at the University. from Vermont.

To overcome these limitations, Albaugh and his colleagues analyzed magnetic resonance imaging data from 799 participants in the Imaging Genetics for Mental Disorders (IMAGEN) study, which followed European adolescents from the age of 14. Participants underwent brain scans at the start of the study and during a 5-year follow-up.

Researchers found that adolescents who reported moderate to high cannabis use tended to have reduced thickness in the left and right prefrontal cortices, an area of ​​the brain involved in planning, decision-making, working memory, and learning. There was a dose-dependent relationship between cannabis use and cortical thickness. That is, those who consumed more cannabis had more cortical thinning in these regions of the brain. This relationship was maintained even after accounting for pre-existing differences in brain structure.

Impaired neurodevelopment also appears to have behavioral consequences. The researchers found that cannabis-related cortical thinning was associated with higher levels of impulsivity.

“Taken together, these results provide strong circumstantial evidence that cannabis use during adolescence is associated with impaired neurodevelopment, particularly in brain cortices rich in cannabinoid receptors 1 and undergoing the greatest change related to age in mid to late adolescence. Our results are consistent with animal research suggesting that adolescence may be a particularly vulnerable time for the effect of tetrahydrocannabinol (THC) on brain structure and function, ”Albaugh told PsyPost.

“The observed brain effects of cannabis in this study may play an important role in the link between cannabis use in adolescents and various negative outcomes, including psychiatric symptoms in adults.”

The researchers controlled for factors such as alcohol consumption, baseline cortical thickness, gender, socioeconomic status, and IQ scores. But it’s still possible that a third factor explains the apparent association between cortical thinning and cannabis use.

“As with all human research on this topic, our study was observational in nature. Accordingly, we cannot exclude the possibility that pre-existing cognitive and / or behavioral differences were associated with the neurodevelopmental trajectories observed and that cannabis use was not causally linked to the development of the cerebral cortex, ”explained Albaugh.

“Although such an alternative explanation is possible, several observations of the present study deserve to be reiterated. First, there was a dose-dependent association at 5 years of follow-up between lifelong cannabis use and cortical thickness. Second, there was no significant association between baseline cortical thickness and lifelong cannabis use at the 5-year follow-up. Third, the spatial pattern of cannabis-related thinning was significantly associated with a PET-derived map of CB1 receptor availability.

The researchers say their findings underscore the importance of conducting longitudinal studies to examine the consequences of cannabis use.

“We are currently examining to what extent cannabis use in early adulthood (ages 19 to 23) affects brain maturation – and, more specifically, whether the brain effects we observed in this study are specific to cannabis use among adolescents, ”Albaugh mentioned. “There is compelling evidence from animal studies that cannabis exposure in adolescents produces qualitatively different brain changes compared to cannabis exposure in adulthood.”

The study, “Association of Cannabis Use during Adolescence With Neurodevelopment,” was published on June 16, 2021.

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