Even nonheavy marijuana use during adolescence disrupted normal cognitive maturation, with amplified effects in teens who were first-degree relatives of schizophrenia patients.
Adolescent psychiatrists, school counselors, parents, and cannabis prevention researchers.
5 of 8 cognitive domainsshowed disrupted development with even nonheavy adolescent marijuana use
What the researchers found
Adolescents with emergent marijuana use showed less age-expected improvement in sustained attention, visuospatial working memory, and executive sequencing. First-degree relatives of schizophrenia patients with marijuana use showed additional deficits in processing speed and executive reasoning.
Why it matters
Most adolescent marijuana research focuses on heavy use, but this study shows even typical, nonheavy use patterns can disrupt critical cognitive development, particularly in genetically vulnerable youth.
The numbers in context
Iowa sample: 211 adolescents (40 first-degree, 54 second-degree relatives, 117 controls), 26.5% with emergent MJ use. Birth cohort: 3,463 children assessed ages 10-15. 5 of 8 cognitive domains significantly affected by emergent MJ use.
How the study worked
Two complementary longitudinal samples: Iowa family study with neuropsychological testing at 0, 18, and 36 months, and a birth cohort with substance use and attention assessments between ages 10-15. Mixed linear models and regression analyses.
Who was studied
211 Iowa adolescents stratified by schizophrenia family history and 3,463 birth cohort children.
What this study cannot tell us
Self-reported marijuana use. Iowa sample is relatively small. Cannot fully control for pre-existing cognitive differences. Two different assessment protocols across samples.
How to read the evidence
Two complementary longitudinal samples provide converging evidence; pre-existing differences cannot be fully excluded.
When this study was published
Longitudinal study with assessments across adolescent development.
The bigger picture
This study challenges the notion that moderate marijuana use is harmless for teens, showing cognitive development disruption even at typical use levels and highlighting particular risk for those with family histories of psychosis.
Replication
Converging evidence from two independent samples strengthens findings.
Funding
Not specified in abstract
Conflicts of interest
Not specified in abstract
Questions still open
- Are these cognitive effects reversible if marijuana use stops?
- Should genetic risk screening inform marijuana prevention targeting?
Read the original research
Recreational Marijuana Use, Adolescent Cognitive Development, and Schizophrenia Susceptibility.
Biological psychiatry global open science, 3(2), 222-232
Citation
Ho, Beng-Choon; Barry, Amy B; Koeppel, Julie A; Macleod, John; Boyd, Andy; David, Anthony; O'Leary, Daniel S. (2023). Recreational Marijuana Use, Adolescent Cognitive Development, and Schizophrenia Susceptibility.. Biological psychiatry global open science, 3(2), 222-232. https://doi.org/10.1016/j.bpsgos.2022.01.008