Adolescents who used both alcohol and cannabis showed faster gray matter decline in five brain regions compared to those using either substance alone, with early onset amplifying the effect.
Parents, educators, adolescent health researchers, neuroscientists
Co-use effects not seen with either substance alone
What the researchers found
Co-use of alcohol and cannabis predicted faster gray matter volume decline (-0.046 to -0.138 cm3/year) in the caudal middle frontal cortex, fusiform, inferior frontal, superior temporal, and supramarginal gyri. These effects were not seen with alcohol or cannabis use alone and were more pronounced with early adolescent onset.
Why it matters
Most brain imaging studies focus on one substance at a time. This study reveals that the combination of alcohol and cannabis poses a greater threat to adolescent brain development than either substance alone.
The numbers in context
724 adolescents; 370 female; decline rate -0.046 to -0.138 cm3/year; 5 affected brain regions; Bonferroni-corrected results
How the study worked
Longitudinal analysis of 724 adolescents (370 female) from the NCANDA study using mixed-effects modeling of brain MRI data across 34 regions of interest, with Bonferroni correction for multiple comparisons.
What this study cannot tell us
Cannot fully rule out pre-existing brain differences that led to substance use. Co-users were not using more alcohol than alcohol-only users, but other confounders may exist.
How to read the evidence
Longitudinal design with a large well-characterized sample, repeated brain imaging, and Bonferroni correction for multiple comparisons.
When this study was published
Published in 2022
The bigger picture
Adolescents who use substances rarely stick to just one. This study suggests that polysubstance effects on the developing brain may be worse than the sum of individual substance effects.
Questions still open
- Are these gray matter changes reversible with abstinence? Does the order of substance initiation (alcohol first vs cannabis first) matter for brain outcomes?
Common questions
Is using alcohol and cannabis together worse for the teen brain?
Does the age of first use matter?
Read the original research
Alcohol and cannabis co-use and longitudinal gray matter volumetric changes in early and late adolescence.
Addiction biology, 27(5), e13208
Citation
Luo, Xi; Yang, James J; Buu, Anne; Trucco, Elisa M; Li, Chiang-Shan R. (2022). Alcohol and cannabis co-use and longitudinal gray matter volumetric changes in early and late adolescence.. Addiction biology, 27(5), e13208. https://doi.org/10.1111/adb.13208
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