Prenatal cannabis use affects brain development

Resume: A new study finds that cannabis exposure during pregnancy may impact brain development and long-term mental health.

Researchers used data from the ABCD study to examine neuroimaging of children exposed to cannabis in utero. They found potential biological mechanisms, including altered brain structure and inflammation, that may contribute to behavioral problems.

The study highlights the complexity of linking prenatal cannabis exposure to later mental health problems.

Key Facts:

  1. Impact of prenatal exposure: Exposure to cannabis in the womb may affect brain development and increase mental health risks.
  2. Neuroimaging insights: Changes in brain structure and inflammation were observed in exposed children.
  3. Complex factors: It remains a challenge to separate the effects of cannabis from genetics and environment.

Source: WUSTL

Scientists are trying to understand how cannabis might affect long-term neurodevelopment when people are exposed to it in the womb. Previous work by WashU researchers Sarah Paul and David Baranger in the Behavioral Research and Imaging Neurogenetics (BRAIN) lab led by Ryan Bogdan found links between prenatal cannabis exposure and potential mental health problems in childhood and adolescence, but potential biological mechanisms that might explain this association were unclear.

In research published in Nature Mental Health This month, Bogdan, Dean’s Distinguished Professor of Psychological & Brain Sciences at Washington University in St. Louis, and postdoctoral researcher Baranger outline some of those potential mechanisms, the intervening biological steps that may play a role in how prenatal cannabis exposure leads to behavioral problems later in life.

It shows a woman, leaves and brains.
“It’s possible that what we’re seeing is an anti-inflammatory effect of cannabis, leading to differences in how the brain is pruned during neurodevelopment,” Bogdan said. Credit: Neuroscience News

“We see evidence that cannabis exposure can impact the developing brain, which is consistent with the associations with mental health,” Baranger said.

Trying to figure out the long-term effects of cannabis exposure during pregnancy is not an easy knot to untangle. There are many confounding factors that influence mental health and behavior.

For example, let’s say someone is exposed to cannabis in the womb and later develops attention deficit disorder as a teenager – how do you distinguish that as a heritable trait, or a trait that is influenced by environmental factors, versus a trait that was influenced by cannabis exposure early in development? Or all three processes might contribute to eventual psychopathology.

Another complication is the increasing prevalence of cannabis use, including among pregnant women, where cannabis use increased from 3 to 7 percent between 2002 and 2017.

Researchers used statistical methods to filter out some of these confounding factors and to provide potential biological measures of the relationship between cannabis use during pregnancy and adolescent behavior.

Nothing can establish causality 100 percent, “but we can look at the plausibility of causality and identifying potential biological correlates that are associated with cannabis exposure and these mental health outcomes suggests that it is plausible,” Bogdan said of the study findings.

Researchers used data from the Adolescent Brain and Cognitive Development (ABCD) Study, an ongoing research project involving nearly 12,000 children in the United States.

As part of that study, researchers collected data on each mother’s substance use before birth and neuroimaging data at ages 9-10 and 11-12. About 370 children were exposed to cannabis before the mother knew she was pregnant, and 195 were exposed both before and after knowing the pregnancy.

The researchers looked at several neuroimaging measures that are important for brain development, including measurements of brain thickness and surface area, as well as measurements of water diffusion in and out of cells. The patterns found in the group of children exposed to cannabis before birth are consistent with possible reductions in neuroinflammation.

“It is possible that we are seeing an anti-inflammatory effect of cannabis, leading to differences in the way the brain is pruned during neurodevelopment,” Bogdan said.

Much has been made of the anti-inflammatory effects of cannabis, but reducing inflammation isn’t always a good thing. It’s all about timing. Too much reduction of inflammation at the wrong time can affect the way the brain is pruned and primed.

Another theory is that cannabis exposure leads to accelerated aging. But don’t expect to find irrefutable biological evidence linking mental health problems to early cannabis exposure.

It might not even be about pruning. It might not be the cannabis use itself, but rather the post-combustion products of smoking cannabis that can cause accelerated aging and subsequent cognitive effects, Bogdan said.

Or it all comes down to sociological factors.

It is challenging to find a clear association that proves that cannabis exposure during pregnancy has negative effects during the teenage years. Retrospective studies are often not feasible.

Baranger notes that the biggest limitation of this dataset is that it is retrospective; mothers reported their cannabis use 10 years ago. He is therefore looking forward to new data from prospective, longitudinal studies that will provide more recent, accurate, and detailed information on cannabis use during pregnancy.

“That may give us more answers to these questions in the future.”

In the meantime, the results of this study confirm that if you’re considering using cannabis during pregnancy, “you should talk to your doctor about your choices and what other options may be available,” Baranger said.

Financing: The research reported in this press release was supported by R01DA54750 (RB, AA). Additional funding included: DAAB (K99AA030808), APM (T32DA015035), AJG (DGE-213989), SEP (F31AA029934), ASH (K01AA030083), ECJ (K01DA051759; BBRF Young Investigator Grant 29571), CER (R01DA046224), AA (R01DA54750), RB (R01DA54750, R21AA027827, U01DA055367). Data for this study were provided by the Adolescent Brain Cognitive Development (ABCD) Study, which was funded by awards U01DA041022, U01DA041025, U01DA041028, U01DA041048, U01DA041089, U01DA041093, U01DA041106, U01DA041117, U01DA041120, U01DA041134, U01DA041148, U01DA041156, U01DA041174, U24DA041123, and U24DA041147 from the NIH and additional federal partners (

The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

About this CUD and developmental neuroscience research news

Author: Lea Shaffer
Source: WUSTL
Contact: Leah Shaffer – WUSTL
Image: The image is attributed to Neuroscience News

Original research: Closed access.
“Prenatal cannabis exposure is associated with local differences in the brain that partially mediate associations with increased psychopathology in adolescents” by Ryan Bogdan et al. Nature Mental Health


Prenatal cannabis exposure is associated with local differences in the brain that partially mediate associations with increased psychopathology in adolescents

Cannabis exposure during pregnancy (PCE) is associated with mental health problems in early adolescence, but the potential neurobiological mechanisms remain unknown.

In a large longitudinal sample of adolescents (ages 9-12 years, N= 9,322–10,186) we found that PCE is associated with localized differences in the gray and white matter of the frontal and parietal cortex, associated white matter tracts, and resting striatal connectivity, even after accounting for potential pregnancy, family, and childhood confounding factors.

Variability in diffusion measurements of the forceps minor and pars triangularis partially mediates longitudinal associations of PCE with attention problems and symptoms of attention deficit hyperactivity disorder.

PCE-related differences in brain development may lead to vulnerability to poorer mental health in early adolescence.

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