Twin Study: Alcohol Use, But Not Cannabis Use, During Young Adulthood Linked with Reductions in Cortical Thickness

Minneapolis, MN: Alcohol consumption, but not the use of cannabis, is associated with changes in brain morphology, according to data published in the journal Biological Psychiatry.

Researchers with the University of Minnesota assessed the relationship between alcohol and cannabis exposure during young adulthood on brain morphology in a population-based sample of 436 twins aged 24 years. 

Authors reported, “Greater alcohol, but not cannabis, misuse was associated with reduced thickness of prefrontal and frontal medial cortices, as well as [the] temporal lobe, intraparietal sulcus, insula, parietal operculum, precuneus, and parietal medial areas.” 

Neuroimaging research indicates that human’s intellectual ability is related to brain structure, including the thickness of the cerebral cortex.

Investigators concluded: “No significant associations between cannabis use and thickness were observed. The lack of cannabis-specific effects is consistent with literature reviews, large sample studies, and evidence that observed cannabis effects may be accounted for by comorbid alcohol.

“This study provides novel evidence that alcohol-related reductions in cortical thickness of control/salience brain networks likely represent the effects of alcohol exposure and premorbid characteristics of the genetic predisposition to misuse alcohol. The dual effects of these two alcohol-related causal influences have important and complementary implications regarding public health and prevention efforts to curb youth drinking.”

The findings are consistent with those of several other studies – such as this 2017 study and this 2015 study – indicating that the use of alcohol, but not cannabis, is associated with negative changes in brain morphology. According to the findings of a literature review of 69 studies published in JAMA Psychiatry, “Associations between cannabis use and cognitive functioning in cross-sectional studies of adolescents and young adults are small and may be of questionable clinical importance for most individuals. Furthermore, abstinence of longer than 72 hours diminishes cognitive deficits associated with cannabis use. Results indicate that previous studies of cannabis youth may have overstated the magnitude and persistence of cognitive deficits associated with marijuana use.”

Full text of the study, “The effects of alcohol and cannabis use on the cortical thickness of cognitive control and salience brain networks in emerging adulthood: A co-twin control study,” appears in Biological Psychiatry. Additional information is available from the NORML fact sheet, “Marijuana exposure and Cognitive Performance.”