Adolescent brain surface area changes after starting alcohol and cannabis differed from alcohol-only users
A longitudinal study of 69 youth scanned before and after substance use initiation found that alcohol-only users showed greater surface area decreases in the medial orbitofrontal cortex than those who used both alcohol and cannabis.
Quick Facts
What This Study Found
Researchers obtained brain scans from 69 adolescents at baseline (ages 12-14, before any substance use) and again at follow-up (ages 17-21).
Participants were split into three groups: alcohol-only initiators, alcohol-plus-cannabis initiators, and minimal-use controls.
All groups showed surface area decreases over time (consistent with normal brain maturation), but the pattern differed by substance use.
A significant group-by-time interaction appeared in three regions: bilateral medial orbitofrontal cortices and right insula. In these areas, the alcohol-only group showed more substantial surface area decreases than the alcohol-plus-cannabis group.
The right medial orbitofrontal cortex finding survived conservative vertex-wise analysis, with the alcohol-only group showing significantly greater surface area reduction compared to the combined alcohol-plus-cannabis group.
Key Numbers
69 youth total (23 per group). Baseline ages 12-14, follow-up ages 17-21. Significant group-by-time interactions in bilateral medial orbitofrontal cortices and right insula. Right medial orbitofrontal cortex finding survived vertex-wise analysis at p < .001.
How They Did This
Longitudinal neuroimaging study with baseline scans before substance use initiation and 6-year follow-up. Groups matched demographically. Used FreeSurfer parcellation of 34 cortical regions per hemisphere. Repeated measures ANCOVA for group comparisons with vertex-wise analysis for confirmation.
Why This Research Matters
This is one of few studies with pre-substance-use baseline brain scans, which helps distinguish pre-existing brain differences from substance-induced changes. The unexpected finding that alcohol-only users showed greater surface area loss than cannabis-plus-alcohol users challenges assumptions about additive brain effects.
The Bigger Picture
Most adolescent brain-substance studies are cross-sectional, making it hard to know whether observed differences existed before substance use began. This longitudinal design with pre-use baselines represents a stronger approach, though the sample size limits firm conclusions.
What This Study Doesn't Tell Us
Small sample size (23 per group) limits statistical power. Groups differed in substance use patterns beyond just the alcohol/cannabis distinction. Surface area is one metric of brain structure and may not capture functional changes. The alcohol-plus-cannabis group may have had different overall exposure levels.
Questions This Raises
- ?Why did alcohol-only users show greater surface area loss than those who also used cannabis?
- ?Could cannabis have a neuroprotective interaction with alcohol in certain brain regions, or is this a statistical artifact of small samples?
Trust & Context
- Key Stat:
- Alcohol-only users showed greater orbitofrontal surface area loss than alcohol-plus-cannabis users
- Evidence Grade:
- Moderate. Longitudinal design with pre-use baselines is strong, but small sample size and inability to control all confounders limit conclusions.
- Study Age:
- Published in 2018. Longitudinal adolescent neuroimaging studies have continued to refine understanding of substance effects on brain development.
- Original Title:
- Adolescent Brain Surface Area Pre- and Post-Cannabis and Alcohol Initiation.
- Published In:
- Journal of studies on alcohol and drugs, 79(6), 835-843 (2018)
- Authors:
- Infante, M Alejandra(2), Courtney, Kelly E(6), Castro, Norma, Squeglia, Lindsay M, Jacobus, Joanna
- Database ID:
- RTHC-01701
Evidence Hierarchy
Follows a group of people over time to track how outcomes develop.
What do these levels mean? →Frequently Asked Questions
Does this mean cannabis protects the brain from alcohol damage?
Not necessarily. The finding that alcohol-only users showed greater surface area decreases could reflect differences in drinking patterns, genetics, or other unmeasured factors between the groups. The sample was small and this finding needs replication before drawing any protective conclusions.
Why is surface area important?
Cortical surface area is a measure of brain structure that reflects the amount of folded cortical tissue. Changes in surface area during adolescence are part of normal development, but unusual patterns may indicate substance-related effects on brain maturation.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-01701APA
Infante, M Alejandra; Courtney, Kelly E; Castro, Norma; Squeglia, Lindsay M; Jacobus, Joanna. (2018). Adolescent Brain Surface Area Pre- and Post-Cannabis and Alcohol Initiation.. Journal of studies on alcohol and drugs, 79(6), 835-843.
MLA
Infante, M Alejandra, et al. "Adolescent Brain Surface Area Pre- and Post-Cannabis and Alcohol Initiation.." Journal of studies on alcohol and drugs, 2018.
RethinkTHC
RethinkTHC Research Database. "Adolescent Brain Surface Area Pre- and Post-Cannabis and Alc..." RTHC-01701. Retrieved from https://rethinkthc.com/research/infante-2018-adolescent-brain-surface-area
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.