Mice exposed to THC before birth showed enlarged brain ventricles as embryos, followed by slower brain growth that persisted into adulthood — with females more affected than males.
Researchers studying prenatal cannabis exposure, anyone interested in how THC affects developing brains, neuroscientists studying sex differences in brain development.
What the researchers found
Using MRI brain scans at nine timepoints from gestation through adulthood, researchers tracked what happened to mouse brains after prenatal THC exposure. The trajectory was consistent and concerning.
THC-exposed embryos first showed ventriculomegaly — enlarged fluid-filled spaces in the brain. After birth, this shifted to a deceleration of overall brain growth that persisted through development and into adulthood. Female mice were more affected than males across multiple measures.
The brain regions most consistently impacted spanned both cortex and subcortex, aligning with observed behavioral changes. THC-exposed neonates showed sex-dependent differences in social behavior, and by adolescence, exposed mice displayed increased anxiety-like behavior.
Electron microscopy confirmed structural changes at the cellular level, providing a biological basis for the behavioral observations and suggesting the effects extend beyond gross brain volume to cellular architecture.
Why it matters
This is one of the most comprehensive longitudinal mappings of prenatal THC's effects on brain development available — tracking the same animals from embryo to adult across nine MRI timepoints. The finding that effects are not transient but sustained into adulthood, and that females may be more vulnerable, adds important detail to the prenatal exposure literature (connecting to RTHC-00226 on molecular brain changes and RTHC-00209 on neurodevelopmental outcomes).
The numbers in context
9 MRI timepoints from gestation to adulthood. Ventriculomegaly observed in embryos. Sustained brain growth deceleration through adulthood. Female mice more affected than males. Behavioral changes: altered social behavior in neonates, increased anxiety-like behavior in adolescents.
How the study worked
Longitudinal study in mice using MRI brain imaging at nine timepoints from gestation to adulthood. Combined with behavioral assays (social behavior in neonates, anxiety-like behavior in adolescents) and electron microscopy for cellular-level analysis. THC was administered prenatally; controls received vehicle.
Who was studied
Mice (C57BL strain) exposed to THC during pregnancy, tracked from gestation to adulthood.
What this study cannot tell us
Animal model — mice metabolize THC differently than humans, and brain development timelines differ significantly. THC doses may not directly translate to human exposure levels. The study cannot account for the complex social and environmental factors that influence human neurodevelopment alongside any biological effects of prenatal exposure.
How to read the evidence
Longitudinal animal study with rigorous multi-modal methodology (MRI, behavioral testing, electron microscopy) — strong within the animal model framework but requires caution when extrapolating to humans.
When this study was published
Published in 2026 in Molecular Psychiatry, representing the current frontier of prenatal THC brain imaging research in animal models.
The bigger picture
The prenatal THC research is building a convergent picture across methods and models. Molecular studies (RTHC-00226) show THC changes brain chemistry at the molecular level. This imaging study shows those changes translate to altered brain structure and growth trajectories. Human neuroimaging studies from the ABCD cohort (RTHC-00241) are beginning to show similar patterns in children. Together, these studies suggest prenatal THC exposure initiates a cascade that begins with molecular disruption and manifests as lasting structural and behavioral differences.
Replication
Not stated in abstract.
Funding
Not reported in abstract.
Conflicts of interest
Not reported in abstract.
Questions still open
- What drives the sex difference in vulnerability — hormonal factors, differences in endocannabinoid system development, or something else? Do the brain growth deficits stabilize in adulthood or continue to diverge? Would different THC doses or exposure windows produce different trajectories?
Read the original research
Impact of prenatal delta-9-tetrahydrocannabinol exposure on mouse brain development: a fetal-to-adulthood magnetic resonance imaging study.
Molecular psychiatry, 31(1), 256-269
Molecular Psychiatry is a well-respected journal focusing on the intersection of neuroscience and psychiatry.
Citation
Cupo, Lani; Vecchiarelli, Haley A; Gallino, Daniel; VanderZwaag, Jared; Bradshaw, Katerina; Phan, Annie; Khakpour, Mohammadparsa; Ben-Azu, Benneth; Guma, Elisa; Fouquet, Jérémie P; Spring, Shoshana; Nieman, Brian J; Devenyi, Gabriel A; Tremblay, Marie-Eve; Chakravarty, M Mallar. (2026). Impact of prenatal delta-9-tetrahydrocannabinol exposure on mouse brain development: a fetal-to-adulthood magnetic resonance imaging study.. Molecular psychiatry, 31(1), 256-269. https://doi.org/10.1038/s41380-025-03189-5
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