A team from the Douglas Research Centre found that high cannabis use during pregnancy can cause delays in fetal brain development that persist into adulthood.
Using advanced magnetic resonance imaging (MRI) techniques, the team observed in mice the effects of prenatal cannabis exposure at different key developmental stages.
Public health agencies warn against cannabis use during pregnancy, but most available data are observational in nature. This study, however, provides biological evidence showing how significant use can disrupt brain growth, from the earliest stages of development into adulthood.
Published in
Molecular Psychiatry, a
Nature Portfolio journal, this preclinical study also highlights the increased potency of cannabis on the market today, addressing a significant gap in understanding the associated risks.
"With cannabis legalization being relatively recent [in Canada], we do not yet have long-term data on new THC-based products," explains Mallar Chakravarty, Full Professor in the Department of Psychiatry, researcher at the Douglas Centre, and senior author of the study. "Our findings offer a first glimpse of the consequences that could manifest in ten or twenty years."
Longitudinal tracking of brain development According to Health Canada, the concentration of THC in dried cannabis has increased from an average of 3% in the 1980s to about 15% in 2022, and the concentration in some strains can reach 30%.
To model heavy use, the research team simulated daily exposure equivalent to one or two joints containing more than 10% THC over a period corresponding to the first trimester of human pregnancy.
They observed changes in development at three life stages:
1. Late pregnancy: The bodies of THC-exposed embryos are smaller and their brain ventricles are larger, a sign of abnormal brain development.
2. Early life: Newborns gain weight more quickly, but brain growth is slowed, indicating a developmental imbalance or delay.
3. Adolescence and adulthood: Brain volume remains lower, especially in females, who also exhibit more anxiety-like behaviors.
"The good news is that many of these developmental delays are mild and could likely be mitigated by a supportive environment," notes Mallar Chakravarty.
3D model of the neonatal brain showing regions with reduced growth (in blue) and those with increased growth in the ventricles (in red). (Source: Lani Cupo)
A novel look at lifelong development The methods used provided a level of precision rarely matched in preclinical studies, the scientists explain.
"This is partly because this type of research requires an immense amount of resources," explains Lani Cupo, first author, who conducted the research over six years for her PhD at McGill University. "We used real-time brain imaging to track development throughout the lifespan, an approach rarely used in mouse studies."
Collaborators from the University of Victoria then used ultra-high-resolution microscopy to observe changes that occurred in brain cells following THC exposure.
For better-informed choices The scientists emphasize that some people use cannabis without knowing they are pregnant, and others use it to relieve nausea or cope with anxiety and depression—conditions that can themselves have harmful effects on pregnancy.
"A pregnancy is never 'perfect'," stresses Mallar Chakravarty. "The goal is not to say what is right or wrong, but to provide the information necessary to enable people to make informed decisions."
A follow-up study will be conducted to determine whether other forms of cannabis—such as edibles, vaping products, and CBD products—have a different impact on the brain.
The study The article "Impact of prenatal delta-9-tetrahydrocannabinol exposure on mouse brain development: a fetal-to-adulthood magnetic resonance imaging study", by Lani Cupo, Mallar Chakravarty et al., was published in the journal Molecular Psychiatry. The study was funded by the Canadian Institutes of Health Research.