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How Cannabis Use During Pregnancy May Harm a Baby's Brain

Medically reviewed by Carmen Pope, BPharm. Last updated on July 9, 2024.

By Dennis Thompson HealthDay Reporter

TUESDAY, July 9, 2024 -- Cannabis use during pregnancy might affect the way a child’s brain develops after birth, a new study says.

Brain imaging of children exposed to cannabis in the womb has revealed patterns consistent with reductions in brain inflammation, researchers reported July 4 in the journal Nature Mental Health.

Too much reduction in inflammation in a child’s brain could interfere with “pruning,” the natural process in which weak or unnecessary neural connections are shed as kids transition from early childhood to puberty, researchers said.

“We see evidence that cannabis exposure may influence the developing brain, consistent with associations with mental health,” said researcher David Baranger, a postdoctoral fellow at Washington University in St. Louis.

The research team earlier found that prenatal cannabis exposure appears to increase a child’s later risk for problems involving mental health, behavior and brain function, according to a 2020 report in JAMA Psychiatry.

However, that earlier study couldn’t pinpoint whether this increased brain risk was due solely to weed exposure, or if it was also influenced by genetics or environment, researchers said.

To draw a finer picture, researchers continued to analyze data from the clinical trial that formed the basis of the earlier findings. The trial involved nearly 12,000 children across the United States, and included brain imaging at ages 9-10 and 11-12.

About 370 kids were exposed to cannabis before their mom knew she was pregnant, and 195 were exposed both before and after she learned of her pregnancy, researchers said.

Researchers found evidence of reduced inflammation in the brains of children whose moms used cannabis, which might have affected their development.

However, the findings don’t completely rule out other possible explanations, Baranger said.

For example, weed exposure in the womb might also cause accelerated aging in the brain, or the other chemicals inhaled when smoking cannabis might cause these developmental effects, he said.

Baranger hopes new data from ongoing studies will offer more accurate and detailed data about the effects of weed use during pregnancy.

In the meantime, women thinking of using weed while pregnant should discuss their choices with their doctor and “what other options there might be,” he said in a university news release.


  • Washington University, news release, July 5, 2024

Disclaimer: Statistical data in medical articles provide general trends and do not pertain to individuals. Individual factors can vary greatly. Always seek personalized medical advice for individual healthcare decisions.

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