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Cannabis-using Mothers Could Increase Psychosis Risk in Their Unborn Children

By Leo Bear-McGuinness

Published: Mar 27, 2019   
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Women who use cannabis while they’re pregnant could increase their unborn child’s likelihood of developing psychosis later in life, according to new research from Washington University in St. Louis.

Published in the journal JAMA Psychiatry, the study suggests that prenatal exposure to cannabis may alter the fetal brain’s endocannabinoid system, which could lead the child to develop psychosis when they’re older.    

“Our research shows that prenatal marijuana exposure after maternal knowledge of pregnancy is associated with a small increase in psychosis proneness during middle childhood or about age 10,” said Jeremy Fine, a psychology undergraduate at Washington University and the study's lead author.

Fine and the paper’s other authors have suggested that pregnant women should be discouraged from using cannabis, citing both their own psychosis research and just how little is known about cannabis’ health effects on a developing fetus. It’s a policy endorsed by leading clinical bodies, including the American College of Obstetricians and Gynecologists, which advises doctors to test their patients for cannabis use and encourage them to quit, whether they use it for medical purposes or not. 

But many expecting mothers aren’t taking heed of these informed opinions. Instead, scores of women report using cannabis to relieve the symptoms of morning sickness

Several recent studies have documented this dramatic rise in pregnant women using marijuana. In one 2018 paper, researchers found past-month marijuana use among American pregnant mothers increased from 2.37 percent to 3.85 percent between 2002 and 2014. Another study from the Kaiser Permanente Northern California, the only large health care system in the US that screen pregnant women for cannabis as a standard self-report, found that the number of marijuana-positive reports nearly doubled between 2009 and 2016, from 4 percent to 7 percent. 

But despite this recorded rise in prenatal marijuana habits, there’s still little research into cannabis’ effects on developing embryos and fetuses. While it’s been known since the 1980s that THC can cross the placenta and reach the fetus, its impact and the effects of other cannabinoids on the unborn are still unknown, which is why Washington University’s recent paper could be so informative.

“Data from rodent studies suggest that the endocannabinoid type 1 receptor, through which the psychoactive effects of THC largely arise, is not expressed until the equivalent of 5-6 weeks of human gestation,” said Fine. “Given that mothers in our study on average learned of their pregnancy at 7.7 weeks, it is plausible that any impact of THC on psychosis risk would not arise until sufficient endocannabinoid type 1 receptors are expressed.”

However, any salient findings should be read with caution; the authors note that the study has many limitations. 

The research’s results were based on data from the Adolescent Brain Cognitive Development (ABCD) study, an ongoing nation-wide study on child health and brain development. From this data, the researchers used survey responses from 3,774 mothers about their marijuana use during 3,926 pregnancies. The risk of psychosis in the 4,361 children born from these pregnancies between was measured using a questionnaire given to the children between ages 8.9 and 11 years. Among these children, only 201 (4.61 percent) reported to have been exposed to marijuana before birth. And of these, just 138 were exposed before their mothers knew they were pregnant.

This small sample size, coupled with the imprecise data on timing, amount, frequency and potency of cannabis exposure, leaves the research’s conclusions far less informed than most other prenatal cannabis studies. But its authors still claim their results add to the growing body of work highlighting marijuana’s negative effects on the unborn. 

“Our research is correlational and as such cannot draw causal conclusions,” said Allison Moreau, study co-author and a graduate student in psychology at Washington University. “However, that the relationship between prenatal marijuana exposure following maternal knowledge of pregnancy was associated with offspring psychosis proneness… increases the plausibility that prenatal cannabis exposure may contribute to a small risk of increased psychosis liability in children.”

Despite its soft foundation, the study’s authors ultimately claim its results evident that expectant mothers should think twice before considering cannabis usage during pregnancy.

“Given increasing cannabis accessibility and potency, as well as growing public perceptions that it's safe to use, it is critical for additional research to understand the potential adverse consequences and benefits of cannabis throughout development and how these associations may arise.” said Ryan Bogdan, associate professor of psychological and brain sciences and senior author of the paper. “In the meantime, evidence that prenatal marijuana use is associated with a small increase in offspring psychosis proneness suggests that marijuana use during pregnancy should be discouraged until more is known.”

Leo Bear-McGuinness

Science Writer & Editor

Leo joined Analytical Cannabis in 2019. From research to regulations and analysis to agriculture, his writing covers all the need-to-know news for the cannabis industry. He holds a Bachelor's in Biology from Newcastle University and a Master's in Science Communication from the University of Edinburgh.


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