Pregnant women who use cannabis may slightly increase the risk their child will develop psychosis later in life, according to a new study.
“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,” says Jeremy Fine, an undergraduate majoring in psychological and brain sciences at Washington University in St. Louis and lead author of the study, which appears in JAMA Psychiatry.
The findings come on the heels of several national studies documenting a dramatic increase in marijuana use by pregnant women, including a 2018 study that found past-month marijuana use among pregnant women in the United States increased 75 percent between 2002 (2.85 percent) and 2016 (4.98 percent).
As more states legalize medicinal and recreational use of cannabis, other reports suggest that many marijuana dispensaries commonly suggest cannabis as a natural cure for pregnancy related nausea.
The role of receptors
The new study suggests that doctors should discourage pregnant women from using cannabis at any time in their pregnancy because experts know so little about its health effects.
The findings also raise new concerns that prenatal exposure to cannabis may pose a greater risk after the fetal brain begins to develop a receptor system for endocannabinoids—part of the naturally occurring neurotransmitter network through which cannabis affects the brain.
“One possible explanation for the finding of increased psychosis risk for marijuana use following, but not before, knowledge of pregnancy is that the endocannabinoid receptor system may not be in place during the early weeks of pregnancy,” says senior author Ryan Bogdan, associate professor of psychological & brain sciences.
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“Prenatal cannabis exposure may be associated with later psychosis proneness in offspring only when there is sufficient fetal endocannabinoid type 1 receptor expression, which may not occur until after many mothers learn they are pregnant.”
Bogdan, who directs the Washington University BRAIN Lab, says the latest findings build on other basic research suggesting that endocannabinoid signaling may contribute to processes, such as neurogenesis and neural migration, that play important roles in early development of brain structure and connections.
“This study raises the intriguing possibility there may be developmental windows during which cannabis exposure may be more likely to increase psychosis risk,” he says.
Tetrahydrocannabinol (THC), which is the principal psychoactive component of marijuana, mimics our body’s endocannabinoids and binds to endocannabinoid receptors to exert its effects. Various studies have confirmed that THC crosses the placental barrier to gain access to the developing fetus.
“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,” Fine says.
“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.”
What are the consequences?
Researchers based their findings on data from the Adolescent Brain Cognitive Development (ABCD) study, an ongoing longitudinal study of child health and brain development with data collection sites throughout the nation.They used data from the initial ABCD baseline data release which included survey responses from 3,774 mothers about marijuana usage during 3,926 pregnancies.
Researchers used a questionnaire administered to the children between ages 8.9 and 11 years to measure risk of psychosis in the 4,361 children born from these pregnancies between 2005 and 2008.
The findings show that among the 4,361 children sampled in this study, 201 (4.61 percent) were exposed to marijuana before birth; of these, 63 were exposed following maternal knowledge of pregnancy.
The researchers acknowledge that the study has many limitations, including the small sample of prenatal cannabis-exposed offspring; potential maternal underreporting of use during pregnancy; imprecise data on timing, amount, frequency, and potency of cannabis exposure; absence of data on whether childhood psychosis proneness links to conversion to psychosis; and lack of data on some potential confounders, such as maternal stress and genetic risk of psychosis among parents.
“Our research is correlational and as such cannot draw causal conclusions,” says coauthor Allison Moreau, a graduate student in psychology.
“However, that the relationship between prenatal marijuana exposure following maternal knowledge of pregnancy was associated with offspring psychosis proneness after accounting for potentially confounding variables—such as maternal education, prenatal vitamin usage, prenatal alcohol and nicotine use, child substance use, and so on—increases the plausibility that prenatal cannabis exposure may contribute to a small risk of increased psychosis liability in children,” Moreau says.
The study provides further evidence that expectant mothers should think twice before considering cannabis use 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.” Bogdan says.
“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.”
The National Institutes of Health funded the work.