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Cannabis use during pregnancy linked to mental, behavioral health issues in kids

New research finds that pot use during pregnancy was connected to increased levels of stress, anxiety, aggression and hyperactivity in young children.
Two women smoke cannabis vape pens at a party in Los Angeles on June 8, 2019
Two women smoke cannabis vape pens at a party in Los Angeles in June 2019.Richard Vogel / AP file

Women who use cannabis during their pregnancies could be putting their children at risk of developing mental health and behavioral problems early in life, a study published Monday finds.

Recent research has shown that heavy cannabis use during pregnancy can harm the fetus. Less clear, however, is the effect of the drug on child development in children born to women who used marijuana while they were pregnant. 

As cannabis use becomes more prevalent, especially during pregnancy, it’s important to learn what the potential risk factors are, said Yasmin Hurd, a neuroscientist at the Icahn School of Medicine at Mount Sinai in New York and the lead author of the new study, published in the journal Proceedings of the National Academy of Sciences.

“It’s not that I think that cannabis is a horrible thing,” she said. “But it is a drug that we need to make sure we understand which individuals may be more vulnerable.”

Participants were part of a bigger research project called the Stress in Pregnancy study, which began in 2009 to examine how stress during pregnancy affects fetal growth and development. Pregnant women were invited to enroll in the study during their second trimesters, and women were asked to participate with their children in follow-up assessments up to four years after birth. 

The new research looked at a subset of 322 mother-child pairs from the larger study, including 71 women who reported using cannabis during pregnancy. In this group, the researchers found that cannabis use during pregnancy was connected to increased levels of stress, anxiety, aggression and hyperactivity in young children. The study also identified genetic changes in the placentas of pregnant cannabis users that directly correlated to the increased anxiety and stress in their young children. 

Hurd and her colleagues found that children born to women who used cannabis while pregnant had higher levels of a stress hormone called cortisol in hair samples compared to children born to nonusers. Children of women who used during their pregnancies had increased anxiety and hyperactivity in behavioral assessments. And young girls whose mothers used cannabis during pregnancy demonstrated higher levels of aggression. 

The scientists also measured the children’s heart rate variability, which is linked to anxiety-related disorders in adults and children. (Heart rate variability is a measure of how well your heart is able to speed up or slow down in response to certain stressors. High heart rate variability is generally considered an indicator of a healthy heart.) They found that children of women who used cannabis during their pregnancies had reduced heart rate variability, suggesting increased susceptibility to anxiety-related disorders. 

Samples taken from placentas also pointed to the effects of cannabis use during pregnancy. The researchers found that placentas from people who used cannabis during pregnancy had reduced expression of several genes associated with immune system function and that the differences were directly correlated with the children’s future anxiety and behavior. 

“I think it’s pretty surprising that they were actually able to detect these effects,” said Patricia Conrod, a clinical psychologist at the University of Montreal, who wasn’t involved in the study. 

“Demonstrating causality on complex processes like this is very difficult to establish,” she said. And while the new research doesn’t go far enough to show that cannabis use during pregnancy leads to problems in children, it provides evidence of a correlation. 

“The focus on biological markers to explain the link between maternal cannabis and child outcomes is convincing, but requires further study before we can causally link maternal cannabis use to child brain health,” Conrod said. 

Indeed, the researchers can’t say for sure whether there is a direct cause-and-effect relationship. However, the consistency of the data is compelling, Hurd said, and the results are in line with results from earlier research showing that cannabis use while pregnant directly affects the fetus. “You can’t ignore that,” she said. 

Cannabis is marketed as a safe substance, said Dr. Salomeh Keyhani, a physician and professor of medicine at the University of California, San Francisco, who wasn’t involved in the study. 

But people often forget that it’s a psychoactive drug, and an understudied one at that, with growing research on potential harms, she said. “This study suggests that cannabis use during pregnancy, just like tobacco and alcohol, is associated with poor early childhood outcomes.”

The results don’t mean that everyone who is exposed to cannabis in utero will have problems or develop anxiety disorders, Hurd said. But it does suggest that cannabis use during pregnancy may put those children at risk for problems with stress and anxiety and that other factors throughout their lives could then exacerbate them.

“I do think that pregnant women and their physicians need to have more discussions about cannabis use, just like they have in terms of alcohol. Then they need to be given the resources to be able to get help for themselves and their children,” she said. “This is not about stigmatizing women. It’s the opposite. … It’s about the more knowledge you have, the more power you have.” 

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