Cannabis Use and ADHD Both Linked to Thinner Brain Cortex, But Through Different Mechanisms | Research

The takeaway

In young adults, persistent ADHD symptoms and frequent cannabis use were each independently associated with thinner cortex in a brain region critical for impulse control.

Read this if you have ADHD and use cannabis, or if you want to understand how cannabis affects brain structure in people with attention difficulties.

114 young adults scanned: ADHD and cannabis use had independent, additive effects on brain cortex thickness.

What the researchers found

Researchers examined the inferior frontal gyrus, a brain region central to stopping yourself from acting impulsively. They found two distinct patterns.

First, people who performed worse on a stop-signal task (Go/No Go) actually had thicker cortex in this region, regardless of whether they had ADHD or used cannabis. This counterintuitive finding suggests that delayed brain maturation, not just less brain tissue, may underlie poor impulse control.

Second, independent of task performance, both persistent ADHD symptoms and more frequent cannabis use were associated with thinner cortex in the same region. These appeared to be separate effects operating through different neural mechanisms.

Why it matters

This is one of the few studies to disentangle the effects of ADHD and cannabis use on brain structure. The finding that both independently affect the same brain region but through distinct mechanisms suggests that cannabis use may compound existing structural differences in people with ADHD.

The numbers in context

The sample included 114 young adults with and without childhood ADHD. Poorer Go/No Go performance correlated with thicker cortex, while persistent ADHD and cannabis use each correlated with thinner cortex in the same region.

How the study worked

The study included 114 young adults, some with childhood ADHD diagnoses, who underwent MRI brain scanning and completed a Go/No Go impulse control task. Researchers used multiple linear regression to test associations between task performance, ADHD status, cannabis use frequency, and cortical thickness and surface area of the caudal inferior frontal gyrus.

What this study cannot tell us

This was a cross-sectional study, so it cannot determine whether cannabis caused cortical thinning or whether people with thinner cortex were more likely to use cannabis. The sample was drawn from a longitudinal ADHD study, which may limit generalizability.

How to read the evidence

Moderate evidence from a well-designed cross-sectional neuroimaging study with a reasonable sample size, though the design cannot establish causation.

When this study was published

Published in 2016. Neuroimaging techniques and analysis methods have continued to advance since this study.

The bigger picture

ADHD and cannabis use frequently co-occur, making it difficult to attribute brain differences to either one alone. By showing that each has an independent structural signature in the same brain region, this study suggests that regular cannabis use may add a separate burden on impulse control circuitry in people who already have ADHD-related brain differences.

Questions still open

Does cannabis-related cortical thinning reverse with abstinence? Do people with ADHD who use cannabis have worse impulse control outcomes than those with ADHD who do not? Would earlier cannabis use onset lead to more pronounced thinning?

Common questions

Does cannabis thin the brain?

This study found an association between more frequent cannabis use and thinner cortex in one brain region, but it cannot prove cannabis caused the thinning. People with thinner cortex may have been more likely to use cannabis.

Is this effect permanent?

This study measured brain structure at one time point, so it cannot answer whether the thinning is reversible. Other research suggests some structural changes may normalize after sustained abstinence.

Read the original research

Go/No Go task performance predicts cortical thickness in the caudal inferior frontal gyrus in young adults with and without ADHD.

Brain imaging and behavior, 10(3), 880-92

View on PubMed ↗Publisher’s paper ↗

Citation

Newman, Erik; Jernigan, Terry L; Lisdahl, Krista M; Tamm, Leanne; Tapert, Susan F; Potkin, Steven G; Mathalon, Daniel; Molina, Brooke; Bjork, James; Castellanos, F Xavier; Swanson, James; Kuperman, Joshua M; Bartsch, Hauke; Chen, Chi-Hua; Dale, Anders M; Epstein, Jeffery N. (2016). Go/No Go task performance predicts cortical thickness in the caudal inferior frontal gyrus in young adults with and without ADHD.. Brain imaging and behavior, 10(3), 880-92. https://doi.org/10.1007/s11682-015-9453-x