ADHD and Cannabis Have Separate Effects on Brain Connectivity in Young Adults | Research

The takeaway

Brain imaging of young adults showed that childhood ADHD and current cannabis use affected different brain networks, and cannabis did not appear to worsen ADHD-related brain changes.

Read this if you have ADHD and use cannabis and want to understand how each affects your brain.

Cannabis use did not exacerbate ADHD-related brain connectivity changes

What the researchers found

This neuroimaging study examined 75 young adults (ages 21-25) followed since childhood as part of the landmark MTA study of ADHD, comparing brain functional connectivity across four groups: ADHD with cannabis use, ADHD without cannabis, non-ADHD with cannabis, and non-ADHD without cannabis.

Childhood ADHD was associated with weakened connectivity in brain networks supporting executive function and motor control, consistent with known ADHD features.

Contrary to expectations, the effects of cannabis use were distinct from those of ADHD, affecting different brain networks. No interactions between ADHD diagnosis and cannabis use were observed, meaning cannabis did not appear to make ADHD-related brain changes worse.

Exploratory analyses linked the ADHD-related brain changes to poorer neurocognitive performance, while cannabis-related changes showed different behavioral correlates.

Why it matters

People with ADHD are at elevated risk for cannabis use, raising concerns that cannabis might compound ADHD-related brain differences. This study provides preliminary reassurance that the two effects are independent, though the small sample size means this finding needs replication.

The numbers in context

75 participants: 23 ADHD + cannabis, 22 ADHD without cannabis, 15 comparison + cannabis, 15 comparison without cannabis. Followed since ages 7-9.9 from the MTA study.

How the study worked

Resting-state fMRI study with a 2x2 design (ADHD vs. comparison x cannabis user vs. non-user) in 75 young adults from the MTA longitudinal study. Intrinsic functional connectivity was measured within 9 functional networks. Participants with ADHD had been followed since age 7-9.9 years.

What this study cannot tell us

Small sample size (especially in comparison groups with only 15 each) limits statistical power. Cross-sectional brain imaging cannot determine causality or temporal ordering. Cannabis use was assessed at one time point without detailed history of use patterns. The study cannot rule out subtle interactions that would require larger samples to detect.

How to read the evidence

Cross-sectional neuroimaging with small sample sizes, especially in control groups. Preliminary evidence requiring replication in larger cohorts.

When this study was published

Published in 2017, with participants from the MTA study followed since the 1990s.

The bigger picture

The independence of ADHD and cannabis effects on brain connectivity suggests these are truly separate influences on brain organization. This has implications for both clinical management (cannabis use may not require different treatment approaches for ADHD patients) and neuroscience (the mechanisms of ADHD and cannabis effects may be biologically distinct).

Questions still open

Would larger studies with more statistical power detect subtle interactions between ADHD and cannabis on brain connectivity? Does the type, frequency, or potency of cannabis matter for ADHD-related brain outcomes? Could cannabis use in adolescence (rather than young adulthood) interact differently with ADHD?

Common questions

Does cannabis make ADHD worse in the brain?

This study found no evidence of that. ADHD and cannabis affected different brain networks independently, and no interactions between the two were detected. However, the small sample size means this finding needs confirmation in larger studies.

How does ADHD affect the brain differently from cannabis?

ADHD was primarily associated with weakened connectivity in executive function and motor control networks, linked to poorer cognitive performance. Cannabis effects were in different networks and showed different behavioral associations.

Read the original research

Distinct effects of childhood ADHD and cannabis use on brain functional architecture in young adults.

NeuroImage. Clinical, 13, 188-200

View on PubMed ↗

Citation

Kelly, Clare; Castellanos, F Xavier; Tomaselli, Olivia; Lisdahl, Krista; Tamm, Leanne; Jernigan, Terry; Newman, Erik; Epstein, Jeffery N; Molina, Brooke S G; Greenhill, Laurence L; Potkin, Steven G; Hinshaw, Stephen; Swanson, James M. (2017). Distinct effects of childhood ADHD and cannabis use on brain functional architecture in young adults.. NeuroImage. Clinical, 13, 188-200.