Cannabis and nicotine had opposite effects on brain cortex thickness in teens and young adults | Research

The takeaway

Among 223 young people aged 16-22, both cannabis and nicotine users had thinner frontal cortices than non-users, but in those who used both substances, cannabis appeared to partially offset nicotine-related thinning.

Neuroscientists, adolescent health researchers, and clinicians working with young substance users

223 participants aged 16-22 scanned with MRI

What the researchers found

Both cannabis and nicotine users had thinner frontal cortices bilaterally compared to non-users. However, an interaction effect was observed: in three left frontal regions, cannabis use was associated with thicker cortices among those with a history of nicotine use, suggesting cannabis may partially offset nicotine-related cortical thinning.

Why it matters

Cannabis and nicotine are frequently co-used by young people, yet most brain studies examine them separately. Understanding how these substances interact during a critical period of brain development has important implications for public health messaging.

The numbers in context

223 participants aged 16-22; 11 bilateral frontal cortical regions examined; interaction effects found in 3 left frontal regions; both substances independently associated with thinner cortices

How the study worked

Cross-sectional study using structural MRI to measure cortical thickness in 11 bilateral frontal regions among 223 participants aged 16-22. Linear regression models examined main and interactive effects of past-year nicotine and cannabis use on gray matter thickness.

What this study cannot tell us

Cross-sectional design cannot determine causality or temporal sequence; cortical thickness differences may precede substance use; cannot rule out other substance use or confounders; self-reported use data

How to read the evidence

Cross-sectional neuroimaging study with appropriate statistical modeling but unable to establish causality or temporal direction.

When this study was published

2024 study

The bigger picture

The interaction between cannabis and nicotine on brain structure suggests studying either substance in isolation may miss important combined effects, especially given how commonly they are used together by young people.

Questions still open

What mechanism could explain cannabis offsetting nicotine-related cortical thinning? Do these structural differences translate into functional or cognitive differences?

Common questions

How did cannabis and nicotine affect brain structure differently?

Both substances were independently associated with thinner frontal cortices compared to non-users. But when researchers looked at people who used both substances, cannabis appeared to partially counteract nicotine-related thinning in three left frontal brain regions.

Why does this interaction matter?

Cannabis and nicotine are frequently used together by teens and young adults, but most research examines them separately. This study suggests their combined effects on the developing brain may be different from what either substance does alone.

Read the original research

The Combined Effects of Nicotine and Cannabis on Cortical Thickness Estimates in Adolescents and Emerging Adults.

Brain sciences, 14(3)

View on PubMed ↗Publisher’s paper ↗

Citation

Hernandez Mejia, Margie; Courtney, Kelly E; Wade, Natasha E; Wallace, Alexander; Baca, Rachel E; Shen, Qian; Happer, Joseph Patrick; Jacobus, Joanna. (2024). The Combined Effects of Nicotine and Cannabis on Cortical Thickness Estimates in Adolescents and Emerging Adults.. Brain sciences, 14(3). https://doi.org/10.3390/brainsci14030195