Summary: Children who were prenatally exposed to cannabis showed a thicker prefrontal cortex compared with children whose mothers did not use cannabis during pregnancy.
Cannabis use during pregnancy is linked to altered brain structure in children, a new study published in Biological Psychiatry reports.
Researchers found that children aged 6 to 8 years who had been exposed to cannabis before birth exhibited increased cortical thickness in frontal regions of the brain, particularly the prefrontal cortex — an area involved in complex cognition, decision-making, and working memory. These findings come from a prospective, population-based neuroimaging study led by Hanan El Marroun at Erasmus University Medical Center in the Netherlands.
“This study is important because cannabis use during pregnancy is relatively common and we know very little about the potential consequences of cannabis exposure during pregnancy and brain development later in life,” said Dr. Hanan El Marroun.
An estimated 2–13% of women worldwide use cannabis while pregnant. Previous research has linked prenatal cannabis exposure to short- and long-term behavioral differences and elevated risk for certain psychopathologies in offspring, but evidence about effects on brain morphology has been limited. The current study aims to fill that gap by examining structural brain measures obtained with magnetic resonance imaging (MRI).
The study population came from the Generation R Study, a large prospective cohort based in the Netherlands that follows children from pregnancy onward. From this cohort, researchers analyzed MRI scans for three groups: 54 children prenatally exposed to cannabis (most of whom were also exposed to tobacco), 96 children exposed prenatally to tobacco only, and 113 unexposed control children matched on age and sex. Structural MRI scans were processed using FreeSurfer to obtain volumetric and cortical thickness measures, and vertexwise analyses and adjusted linear regression models were applied to test associations while accounting for relevant covariates.
Key findings:
- No significant differences were observed in global brain volume measures (total brain, gray matter, or white matter volume) among cannabis-exposed children compared with controls.
- Cannabis exposure during pregnancy was associated with localized increases in cortical thickness in frontal brain regions, particularly the prefrontal cortex, when compared with nonexposed children.
- By contrast, prenatal tobacco exposure alone was associated with cortical thinning in areas such as the superior frontal and superior parietal cortices, indicating that cannabis and tobacco may have different effects on cortical development.
Dr. John Krystal, Editor of Biological Psychiatry, highlighted the public health relevance: “The growing legalization, decriminalization, and medical prescription of cannabis increases the potential risk of prenatal exposure. This important study suggests that prenatal exposure to cannabis could have important effects on brain development.”
At the same time, the authors caution against overinterpretation. Dr. El Marroun emphasized the need for more research to determine whether the associations observed are causal and to clarify mechanisms. Because most children in the cannabis-exposed group were also exposed to tobacco, disentangling independent and combined effects requires further study.
Despite limitations, the study contributes to an emerging literature that links prenatal substance exposure to measurable differences in brain structure and supports public health efforts to reduce cannabis and tobacco use during pregnancy. The authors and editors recommend careful consideration of substance use during pregnancy and further investigation into how prenatal exposures influence long-term cognitive and behavioral outcomes.
Study details: “Prenatal Cannabis and Tobacco Exposure in Relation to Brain Morphology: A Prospective Neuroimaging Study in Young Children” by Hanan El Marroun and colleagues, published in Biological Psychiatry (online June 2016). The study analyzed MRI-derived brain volumetric and cortical thickness measures from children aged 6–8 years enrolled in the Generation R Study in the Netherlands.
Funding and disclosures: Authors’ institutional affiliations and disclosures of financial and potential conflicts of interest are reported in the article.
Abstract (condensed)
Background: Prenatal cannabis exposure has been linked to behavioral differences in offspring, but its effects on brain structure are not well established. This prospective study examined associations between prenatal cannabis exposure and brain morphology in young children.
Methods: MRI scans from children aged 6–8 years were analyzed for cortical thickness and volumetric measures. The sample included 54 children with prenatal cannabis exposure (mostly also exposed to tobacco), 96 children prenatally exposed to tobacco only, and 113 nonexposed controls. FreeSurfer-based vertexwise and regression analyses adjusted for relevant covariates.
Results: Prenatal cannabis exposure was not associated with differences in global brain volumes. However, cannabis-exposed children showed increased cortical thickness in frontal regions compared with nonexposed controls. Prenatal tobacco exposure was associated with cortical thinning in superior frontal and parietal areas.
Conclusions: These findings suggest an association between prenatal cannabis exposure and altered cortical thickness in children. Further research is needed to determine causality and to explore developmental and functional consequences.