Marijuana and Pregnancy: What are the Risks?

The use of marijuana (cannabis) has become a widely debated topic in the United States in recent times, and most have strong opinions about the medicinal or recreational use of this powerful plant. As some women consider using marijuana to treat issues such as morning sickness they are left wondering about the effects of marijuana on themselves and their baby while pregnant. In this piece, author Pamela McColl shares a few reasons that using marijuana during pregnancy may have detrimental effects on the child, and why it should be avoided, even as a medical treatment, during this critical time.

The public discussion and debate over marijuana, both as a recreational drug and for medicinal use, rages on. Negotiating through the rhetoric has left many of us searching for an objective, evidence based discussion. In the context of maternity and marijuana there are specific, recent scientific findings that can assist in making appropriate choices for the well-being of mother and child. We now have solid scientific findings that demonstrate that marijuana is not harmless, but a potent drug that can cause harm to the brain maturation in the fetus.  It is critically important to understand the science of marijuana use in pregnancy to protect both mother and child.

Marijuana use during pregnancy interrupts fetal brain development. This can result in permanent damage and compromise the development of future cognitive abilities (1). It is the tetrahydrocannabinol (THC), the active ingredient in marijuana, that impacts the growth of the brain and this stage of the brain’s development. Research conducted at the Icahn School of Medicine at Mount Sinai Hospital in New York, along with studies at the Medical University of Vienna and the Karolinska Institute in Stockholm, demonstrated that fetuses exposed to cannabis showed significantly lower levels of the protein needed for the development of cognitive abilities required to conduct planning, memory, decision making and organization functions.

Pregnant women need to know of the risks associated with marijuana use on the fetal brain and if they are using this drug either recreationally or for a relief of nausea associated with morning sickness. Smoking marijuana during pregnancy has been shown to decrease baby’s birth weight, most likely due to the effects of carbon monoxide on the developing fetus (2).  According to Dr. Andra Smith, Associate Professor at the University of Ottawa, School of Psychology: Yes, it might make the morning sickness subside but at what cost? The long term consequences may well be far more damaging than the short term relief. Marijuana crosses the placental barrier and has subtle effects on the newborn baby. However, it is the longer lasting and more delayed effects on cognitive processing that are most alarming. The prenatal exposure to cannabis contributes to a vulnerability of neurocognitive functioning that has been observed as early as 3 years of age and most strikingly continuing into young adulthood.

The growing evidence for a negative impact of prenatal cannabis exposure originates from three longitudinal studies worldwide. Due to the wide range of lifestyle variables that contribute to both brain, body and mental health, prospective studies are required to ensure control of as many of these variables as possible. This is the methodology that has been used for the Ottawa Prenatal Prospective Study (OPPS; 9) in Canada, the Maternal Health Practices and Child Development Project (MHPCDP; 10) in the US and the Generation R study in Europe (11).

Each of these studies investigated prenatal marijuana exposure in varying samples with different testing measures, and for these reasons all results are not comparable. However, the significant results that are consistent across the OPPS and MHPCDP, the two studies that have tested children for the longest period of time, and include neurocognitive challenges in the areas of short-term memory, as well as verbal outcomes, aspects of attention, impulsivity and abstract visual skills (9,10,12,13). These deficits appear after age 3 and continue into young adulthood (14,15). Most significantly, at 6 years of age, children exposed prenatally to marijuana showed more impulsive and hyperactive behaviour. This continued into adolescence and was accompanied by problems in abstract and visual reasoning, as well as visuo-perceptual functioning. These are the types of skills required to perform “top down processing”, such as good decision making, organizing behaviour, setting goals and putting into action a plan to accomplish the goals. Each of these cognitive processes can be grouped under the umbrella term of executive functioning.

Executive functioning is required for success in life, including schooling, relationships and work life. Struggles can occur in these facets when executive functions are compromised, something that can occur with prenatal marijuana exposure (16). Regular use during pregnancy is cause for concern.

In summary, prenatal marijuana exposure does have negative consequences on both the mother and child. This impact should be known so that expectant mothers can make informed choices about how to treat their morning sickness and ultimately care for the future of their children.

Pamela McColl is a doula, tobacco prevention activist, author and publisher. In 2012, she published the first smoke-free edition of the famous poem “Twas The Night Before Christmas” to generate more discussion and awareness of the cultural influences that impact young children and their future use of tobacco products. The publication won seven book awards including four Benjamin Franklin Book Awards, a Moonbeam, a gold for Mom’s Choice Awards and a Global International Ebook Award. Working on Baby and Me Tobacco Free brought Pamela’s experience as a labor support doula and prenatal yoga to the discussion of tobacco cessation. Pamela continues to promote the need for greater prevention, education and assistance to those who find themselves wanting to stop the use of tobacco products.


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[15] Smith, A.M., Fried, P., Hogan, M., Cameron, I. (2004). Effects of prenatal marijuana exposure on response inhibition: An fMRI study of young adults. Neurotoxicology and Teratology. 26(4), 533-542.

[16] Fried, P.A. & Smith, A. (2001). A literature review of the consequences of prenatal marihuana exposure: an emerging theme of a deficiency in aspects of executive function. Neurotoxicology and Teratology. 23, 1-11.