The Effects of Prenatal Marijuana Exposure

Marijuana is the most pervasive recreational drug in America. We have started to see a shift towards legalization of the substance due to its mild effects and potential health benefits for users. The commonality of the drug and blasé regard for it has increased the chance that women who are pregnant will use it. Compared to other drugs and alcohol which have well documented and known impacts on fetal development, research into how marijuana affects the fetus is less widely known because it has no phenotypic expression.[1][3]

Foundational Research

There were two major longitudinal studies performed to investigate the effects of PME, the Ottawa Prenatal Prospective Study (OPPS) and the Maternal Health Practices and Child Development Study (MHPCD). The studies found that PME predicts deficits in memory and attention, increases in attention deficit hyperactive disorder, and symptoms of anxiety in childhood. These two studies are the basis of much of the PME research today. The foundation of this research has been expanded upon in the investigation of Cannabis Use Disorder (CUD). Cannabis Use Disorder is a continued use of marijuana even when it produces signficant stress, anxiety, and impairment. Sonon, Richardson, et al. published a study in the Neurotoxicology and Teratology Journal that affirmed the conclusions of the OPPS and MHPCD studies finding that PME was associated with early onset of marijuana use, indirectly contributing to CUD. The early onset would lead to depressive symptoms in adolescents and it was concluded that the pathway of PME to early use and depressive symptoms were the major contributing factors in CUD. However, the connection was not direct from PME predicting CUD.

Teratogens and the Sensitive Period

The term Teratogen is used to describe a factor that causes malformation of an embryo. Typically teratogens have periods during pregnancy where their impacts are the most pronounced on the embryo, this is called the “Sensitive Period”. Marijuana usage starts to impact the embryo around week eight of prenancy where the endogenous cannabinoid signaling system (ECSS) starts to develop. The ECSS is part of almost every brain structure and organ system and evidence shows is function is to regulate the cardiovascular processes. When an embryo is exposed to Delta-9-tetrahydroacnnabinol (THC) it can alter neurological development and change ECSS pathways.[3]

A study published in the Journal of the American Academy of Child and Adolescent Psychiatry found that heavy marijuana exposure during the first trimester was associated with lower verbal reasoning scores on the Stanford-Binet Intelligence Scale. The study also found that use during the second trimester predicted deficits in short-term memory and quantitiative scores. Use in the third trimester only had significant impact on quantitiatve scores.[2] This would indicate that the highest potential for disruption is in the first trimester and that disruption decreases as the baby comes closer to term. However, it cannot be understated that usage in the third trimester still impacted cognitive development of the child.

Marijuana’s sensitive period is from week 8 through the third trimester

Frequency Dependence

The frequency in which the pregnant mother uses cannabis has a correlation with the impacts on fetus development. The Generation R study, a prospective cohort study that followed people from fetus to young adulthood, gathered data on 7,452 mothers over the course of their pregnancy. The study asked them the frequency of marijuana use and collected the birth weight of the children. The study found that effects on growth reduction of the fetus were the most pronounced when frequency of usage was high throughout the course of history. Mothers who used only a few times during pregnancy resulted in a negligible impact on birth weight.

The frequency effects exhibited here are not exclusive to the Generation R study. Many studies have found a similar conclusion, a higher frequency of use throughout pregnancy exacerabates the effects. The Leech, Larkby et al. study on depression and PME correlation of children age 10 found that heavy use was a better predictor.[4]

Outcomes of Prenatal Marijuana Exposure

Marijuana use will only increase as legalization across America and capitalization of the product occurs. The timelineness of this issue is critical as many people see marijuana use as inoccuous. Across multiple longitudinal studies that have examined areas such as congition, birth weight, behavior, and depression have concluded that prenatal marijuana exposure does impact fetal development. The lack of a phenotypic expression like with fetal alchol syndrome has made the dissemination of information about cannabis use during pregnancy difficult. But mothers, fathers and the public need to hear the message and know that the choices they make can impact their child who has no choice in the matter.


[1] Journal of Neurotoxicology and Teratology, Volume 47, January-February 2015, Pages 10-15 Prenatal marijuana exposure predicts marijuana use in young adulthood

[2] Goldschmidt, L., Richardson, G. A., Wilford, J., & Day, N. L. (2008). Prenatal marijuana exposure and intelligence test performance at age 6. Journal of the American Academy of Child and Adolescent Psychiatry, 47(3), 254.

[3] Journal of Neurotoxicology and Teratology, Volume 58, November-December 2016, Pages 5-14 Prenatal cannabis exposure - The “first hit” to the endocannabinoid system

[4] Leech, S. L., Larkby, C. A., Day, R., & Day, N. L. (2006). Predictors and correlates of high levels of depression and anxiety symptoms among children at age 10. Journal of the American Academy of Child and Adolescent Psychiatry, 45(2), 223.