A systematic review of 12 studies found evidence that nicotine co-use may conceal cannabis-related cognitive impairments in adolescents and young adults, while neuroimaging research on co-use remains scarce.
Neuroscience researchers studying adolescent brain development and clinicians working with young substance users.
Only 12 studies out of 1,107 examined co-use effects on the brain
What the researchers found
Cannabis and nicotine showed independent negative cognitive effects, but when used together, nicotine appeared to mask some cannabis-related cognitive deficits. Preliminary neuroimaging evidence pointed to hippocampal volume differences in co-users. No structural neuroimaging studies examined cannabis-nicotine co-use in adolescent-only populations.
Why it matters
Cannabis and nicotine are frequently co-used, especially among young people. If nicotine masks cannabis-related cognitive problems, studies that do not account for co-use could systematically underestimate cannabis effects on the developing brain.
The numbers in context
1,107 articles screened, 12 met inclusion criteria. Age range: 13-35 years. Preliminary evidence for hippocampal volume differences in co-users. No adolescent-only structural neuroimaging studies found.
How the study worked
Systematic review searching peer-reviewed articles for studies examining cannabis and nicotine/tobacco co-use in ages 13-35 (or nonadult animal subjects). From 1,107 initial articles, 12 met inclusion criteria requiring joint consideration of both substances and neurocognitive or neuroimaging outcomes.
What this study cannot tell us
Only 12 studies met criteria, limiting conclusions. Most studies were cross-sectional. No longitudinal studies specifically designed to examine co-use effects on brain development. Cannot determine mechanisms of the masking effect.
How to read the evidence
Systematic review with rigorous methods, but limited by the small number of qualifying studies and their mostly cross-sectional designs.
When this study was published
2021 systematic review of available literature.
The bigger picture
The masking effect has practical implications. If nicotine compensates for some cannabis-related cognitive deficits, young people who use both substances may not notice cognitive problems until they quit nicotine. This also means existing research that does not separate co-users may have underestimated cannabis harms.
Questions still open
- What is the neurobiological mechanism behind nicotine masking cannabis cognitive effects? Does the masking persist long-term or only acutely? Would vaping nicotine produce the same masking effect as combustible tobacco?
Common questions
Does nicotine protect the brain from cannabis effects?
Why is this finding important for research?
Read the original research
The Influence of Cannabis and Nicotine Co-use on Neuromaturation: A Systematic Review of Adolescent and Young Adult Studies.
Biological psychiatry, 89(2), 162-171
Citation
Hernandez Mejia, Margie; Wade, Natasha E; Baca, Rachel; Diaz, Vanessa G; Jacobus, Joanna. (2021). The Influence of Cannabis and Nicotine Co-use on Neuromaturation: A Systematic Review of Adolescent and Young Adult Studies.. Biological psychiatry, 89(2), 162-171. https://doi.org/10.1016/j.biopsych.2020.09.021
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