Marijuana use during pregnancy: The cannabis conundrum

Marijuana use
© Rafael Ben Ari |

Dennis R. Carty, Ph.D. and Pamela J. Lein, Ph.D., University of California, highlight the rising trend of marijuana use during pregnancy and the implications surrounding it

Many women suffer from nausea and vomiting during pregnancy to the point that these symptoms interfere with daily activities, or in extreme cases, compromise the health of the mother and unborn child. It is perhaps no surprise then that options for relieving these symptoms are a prominent topic in on-line forums for pregnant women. A notable trend in these on-line discussions is increasing advocation for the use of marijuana, also known as cannabis, to relieve pregnancy-induced nausea and vomiting. The mounting interest is driven in part by increasing legalisation and social acceptance of marijuana and approved medical use of cannabis-based products to treat nausea and pain associated with cancer, multiple sclerosis, Crohn’s disease and some forms of epilepsy.

Additionally, marijuana is often promoted as a natural remedy with minimal side effects and, therefore, many women perceive it as a healthier alternative to the standard medications used to treat pregnancy-induced nausea. Indeed, 70% of women recently surveyed in the United States believe that there is “slight or no risk of harm” in cannabis use during pregnancy. The truth is that there are more questions than answers about the safety of marijuana use during pregnancy.

While humans have used marijuana (Cannabis sativa) for recreational, religious, and medicinal purposes for several millennia, basic research regarding the therapeutic efficacy and toxicity of the active constituents in cannabis, such as tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD), is remarkably limited. The basis of marijuana’s biological effects was not determined until the 1990s when neuroscientists discovered two cannabinoid receptors, CB1R and CB2R, in the mammalian brain.

Subsequently, researchers found that these receptors respond to molecules naturally synthesized in the body from fatty acids, which are called endogenous cannabinoids, or endocannabinoids. The endocannabinoid system functions to regulate numerous physio­logical processes, including body temperature, hunger, processing of sensory information, and cognition.

Cannabis is a complex mixture of pharmacologically active compounds that includes more than 100 cannabinoids in addition to Δ9-THC and CBD, as well as other pharmacologically active molecules, such as terpenes and flavonoids. These compounds interact with the endocannabinoid system to cause the biological effects associated with cannabis.

For example, the binding of Δ9-THC to CB1R causes the “high” associated with smoking or ingesting marijuana. CB1R is widely expressed in the developing brain, and data from experimental animal models indicate that endocannabinoid signalling plays a significant role in the normal development of the brain. Either overstimulating or blocking CB1R activity during brain development causes “miswiring” of brain circuits. This altered brain circuitry manifests as behavioural deficits in the young animal that persist into adulthood.

CB1R is expressed in the developing human brain by the first weeks of the second trimester. Δ9-THC, CBD and other cannabinoids in marijuana cross the placenta and are transferred into breast milk. Because cannabinoids have a relatively long half-life in the human body, the fetus or breast-feeding infant may be exposed to active cannabinoids for up to 5 days after maternal use of cannabis.

Such observations raise the possibility that marijuana use during pregnancy potentially alters fetal or infant brain development by interfering with the endocannabinoid signalling system in the developing brain. This possibility is supported by data emerging from several large epidemiological studies of cannabis use during pregnancy in North America and Europe.

These studies report an association between maternal cannabis use and increased impulsivity, attention deficit, hyperactivity, delinquent behaviours, and impaired memory in children, and higher rates of depression, drug abuse, memory deficits, and psychosis in adolescents and adults.

A key question is whether there is a safe level of maternal marijuana use. Answering this question requires knowing how much marijuana is consumed by women during pregnancy. However, quantifying marijuana intake is challenging because the potency of cannabis, as well as the ratio of the different active cannabinoids it contains, is extremely variable. With regard to the latter, it is also unknown as to which constituent(s) in marijuana impact the developing brain.

This is a critically important question in light of widespread on-line discussions suggesting that CBD is safer than Δ9-THC. Compared to the significant amount of research on the toxicity of Δ9-THC, which is linked to the dysphoric and other adverse effects of marijuana abuse, there has been comparatively little research on the potential toxicity of CBD.

Recent studies in zebrafish, which have an active endocannabinoid system, suggest that CBD causes abnormal development and lethality at concentrations significantly lower than Δ9-THC. While it has yet to be determined whether CBD interferes with brain development in mammals, including humans, these findings suggest the urgent need for research to characterize the developmental neurotoxicity potential of the individual active constituents in marijuana.

The developmental neurotoxicity of marijuana is also influenced by the production and method of consumption of cannabis products. For example, smoking a cannabis cigarette produces combustion byproducts, including polycyclic aromatic hydrocarbons (PAHs), which are neurotoxic to the developing brain. Vaporizing dried cannabis significantly reduces the production of combustion byproducts, but can introduce neurotoxic metal contaminants into the inhaled product and increase the amount of active cannabinoid consumed.

Concentrates such as oils, tinctures, and edibles avoid the issues associated with smoking or vaping cannabis. However, these methods of consumption do not mitigate the problem of wide variability in the purity of cannabis products.

For example, cultivation practices can introduce contaminants such as microbial impurities, mycotoxins, metals, and pesticides into the final product. Maternal consumption of cannabis products containing these contaminants can result in their transfer to the fetal brain, which is of potential concern since many of these contaminants are known to interfere with brain development.

As cannabis use becomes increasingly acceptable and widespread, increasing numbers of women are likely to use cannabis during pregnancy. While the impact of maternal cannabis use on the unborn child remains an open question, the data that are currently available warrant caution, and underscore the urgent need for additional research to inform ongoing discussions regarding the cannabis conundrum in pregnancy.


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Dennis R. Carty, Ph.D

Post Doctoral Scholar


Pamela J. Lein, Ph.D

Professor and Chair

Department of Molecular Biosciences


UC Davis CounterACT Center of Excellence


University of California, Davis

Tel: +1 530 752 1970


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