You would be hard-pressed to track down advisings calling for pregnant persons to pay a celebratory visit to their local dispensary. While most Americans support marijuana legalization, the notion of pregnant women lighting up a joint still ignites controversy (Jones, 2022). Nevertheless, the rate of prenatal cannabis exposure has increased over the last twenty years (Volkow et al., 2019), a trend that seems to have only accelerated during the COVID-19 pandemic (Young-Wolff et al., 2021). Little wonder, then, that the study of in-utero cannabis exposure remains such a lively area of research—while society grapples with marijuana’s changing role, science is left to explore the hazy frontiers of its impact on fetal development. And hazy it is!

Prominent researchers and health organizations strongly caution against cannabis consumption during pregnancy, pointing to adverse effects on the developing brain (American College of Obstetricians and Gynecologists, 2017; Young-Wolff et al., 2021). The potential for harm lies in the ability of tetrahydrocannabinol (THC), an exogenous cannabinoid and the primary psychoactive compound in cannabis, to traverse the placental barrier into the fetal circulation (Bailey et al., 1987; Behnke et al., 2013; Nashed et al., 2021). With cannabinoid receptors active in the developing fetus, THC could disrupt the developing endocannabinoid system, which is critical in guiding neural maturation during crucial periods of growth (Galve-Roperh, 2009; Harkany et al., 2008). In particular, the prefrontal cortex—responsible for executive function and impulse control—develops prenatally and throughout adolescence (Selemen & Zecevic, 2015) under the guidance of the endocannabinoid system (Ahmad et al., 2017; Kruk-Slomka et al., 2017). Thus, prenatal cannabinoid exposure may impact the formation of fetal neural systems essential for higher-order cognitive functions (Tirado-Muñoz, 2020).

Evidence consistently supports associations between specific fetal outcomes and cannabis consumption, such as low birth weight and neonatal intensive care unit admission (Gunn et al., 2016; Marchand et al., 2022). However, study findings are mixed regarding the impact on other measures of neurodevelopment related to executive functioning, such as working memory, attention, and impulse control. Fried et al. (1992) found that 6-year-old children subjected to cannabis in the womb exhibited impaired impulse control and attention span. Similarly, Goldschmidt et al. (2008) observed that 6-year-old children with prenatal marijuana exposure demonstrated lower intellectual development than children without exposure.

Diverging from the reports of Fried et al. (1992) and Goldschmidt et al. (2008), Murnan et al. (2021) reported that 3.5-year-old children with intrauterine cannabis exposure showed no signs of atypical executive functioning. Corroborating these results, Moore et al. (2023) found no evidence that prenatal exposure adversely affected the cognitive abilities of 5-year-olds with prenatal marijuana exposure. In fact, some data even point to positive associations between specific cognitive outcomes and prenatal cannabis exposure, including attention (Leech et al., 1999).

Though study results are mixed and muddled, the medical establishment largely warns against cannabis during pregnancy—leaving the public in doubt about what science really says (Chasnoff, 2017; Office of the Surgeon General, 2019). For better or for worse, laypeople are not alone in their uncertainty. Casting doubt on the growing body of studies asserting that children exposed to cannabis in the womb exhibit diminished cognitive abilities compared to their unexposed peers, Torres et al. (2020) conducted a comprehensive analysis of research exploring the effects of prenatal marijuana exposure on cognitive development. Scrutinizing over 1,000 statistical comparisons across the gamut of research, Torres and colleagues found scant evidence that prenatal cannabis exposure substantially hampered brain development. The scattered disparities surfaced were minor, with the thinking skills of cannabis-exposed children overwhelmingly falling within normal bounds.

When it comes to prenatal cannabis, the fog of scientific uncertainty lingers thick. Conflicting findings are aplenty, with some studies showing no significant neurodevelopmental differences in cannabis-exposed children, while others point to disparities in areas like impulse control, inattention, and memory. However, where fetal development is concerned, even minor discrepancies merit a pause—and call for balancing an open mind with a critical eye. The reality is likely complex, but with time and unbiased effort, the truth will out—blowing the smoke away, as it were. As cannabis becomes mainstream, we need facts, not fear-mongering; evidence, not exaggerations. When it comes to pregnancy, prudence prevails. But where facts end and speculation begin, we would be wise to tread carefully.

References

Ahmad, T., Sun, N., Lyons, D., & Laviolette, S. R. (2017). Bi-directional cannabinoid signaling in the basolateral amygdala controls rewarding and aversive emotional processing via functional regulation of the nucleus accumbens. Addiction Biology, 22(5), 1218–1231. https://doi.org/10.1111/adb.12406

American College of Obstetricians and Gynecologists. (2017). Committee opinion no. 722 summary: Marijuana use during pregnancy and lactation. Obstetrics & Gynecology, 130(4), 931–932. https://doi.org/10.1097/aog.0000000000002349

Bailey, J. R., Cunny, H. C., & Slikker, W., Jr. (1987). Fetal disposition of delta 9-tetrahydrocannabinol (THC) during late pregnancy in the rhesus monkey. Toxicology and Applied Pharmacology, 90(2), 315–321. https://doi.org/10.1016/0041-008x(87)90338-3

Behnke, M., Smith, V. C., Committee on Substance Abuse, & Committee on Fetus and Newborn. (2013). Prenatal substance abuse: Short- and long-term effects on the exposed fetus. Pediatrics, 131(3), e1009–e1024. https://doi.org/10.1542/peds.2012-3931

Chasnoff, I. J. (2017). Medical marijuana laws and pregnancy: Implications for public health policy. American Journal of Obstetrics and Gynecology, 216(1), 27–30. https://doi.org/10.1016/j.ajog.2016.07.010

Fried, P. A., Watkinson, B., & Gray, R. (1992). A follow-up study of attentional behavior in 6-year-old children exposed prenatally to marihuana, cigarettes, and alcohol. Neurotoxicology and Teratology, 14(5), 299–311. https://doi.org/10.1016/0892-0362(92)90036-a

Galve-Roperh, I., Palazuelos, J., Aguado, T., & Guzmán, M. (2009). The endocannabinoid system and the regulation of neural development: Potential implications in psychiatric disorders. European Archives of Psychiatry and Clinical Neuroscience, 259(7), 371–382. https://doi.org/10.1007/s00406-009-0028-y

Goldschmidt, L., Richardson, G. A., Willford, 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), 18216735. https://doi.org/10.1097/chi.0b013e318160b3f0

Gunn, J. K., Rosales, C. B., Center, K. E., Nuñez, A., Gibson, S. J., Christ, C., & Ehiri, J. E. (2016). Prenatal exposure to cannabis and maternal and child health outcomes: A systematic review and meta-analysis. BMJ Open, 6(4), e009986. https://doi.org/10.1136/bmjopen-2015-009986

Harkany, T., Keimpema, E., Barabás, K., & Mulder, J. (2008). Endocannabinoid functions controlling neuronal specification during brain development. Molecular and Cellular Endocrinology, 286(1-2 Suppl 1), S84–S90. https://doi.org/10.1016/j.mce.2008.02.011

Jones, J. M. (2022, December 15). Marijuana views linked to ideology, religiosity, age. Gallup. https://news.gallup.com/poll/405086/marijuana-views-linked-ideology-religiosity-age.aspx

Kruk-Slomka, M., Dzik, A., Budzyńska, B., & Biala, G. (2016). Endocannabinoid system: The direct and indirect involvement in the memory and learning processes—a short review. Molecular Neurobiology, 54(10), 8332–8347. https://doi.org/10.1007/s12035-016-0313-5

Leech, S. L., Richardson, G. A., Goldschmidt, L., & Day, N. L. (1999). Prenatal substance exposure. Neurotoxicology and Teratology, 21(2), 109–118. https://doi.org/10.1016/s0892-0362(98)00042-7

Marchand, G., Masoud, A. T., Govindan, M., Ware, K., King, A., Ruther, S., Brazil, G., Ulibarri, H., Parise, J., Arroyo, A., Coriell, C., Goetz, S., Karrys, A., & Sainz, K. (2022). Birth outcomes of neonates exposed to marijuana in utero. JAMA Network Open, 5(1), e2145653. https://doi.org/10.1001/jamanetworkopen.2021.45653

Moore, B. F., Salmons, K. A., Hoyt, A. T., Swenson, K. S., Bates, E. A., Sauder, K. A., Shapiro, A. L. B., Wilkening, G., Kinney, G. L., Neophytou, A. M., Sempio, C., Klawitter, J., Christians, U., & Dabelea, D. (2023). Associations between prenatal and postnatal exposure to cannabis with cognition and behavior at age 5 years: The healthy start study. International Journal of Environmental Research and Public Health, 20(6), 4880. https://doi.org/10.3390/ijerph20064880

Murnan, A. W., Keim, S. A., Yeates, K. O., Boone, K. M., Sheppard, K. W., & Klebanoff, M. A. (2021). Behavioral and cognitive differences in early childhood related to prenatal marijuana exposure. Journal of Applied Developmental Psychology, 77(1). https://doi.org/10.1016/j.appdev.2021.101348

Nashed, M. G., Hardy, D. B., & Laviolette, S. R. (2021). Prenatal cannabinoid exposure: Emerging evidence of physiological and neuropsychiatric abnormalities. Frontiers in Psychiatry, 11(1). https://doi.org/10.3389/fpsyt.2020.624275

Office of the Surgeon General. (2019). U.S. Surgeon General’s advisory: Marijuana use and the developing brain. U.S. Department of Health and Services. https://www.hhs.gov/surgeongeneral/reports-and-publications/addiction-and-substance-misuse/advisory-on-marijuana-use-and-developing-brain/index.html

Selemon, L. D., & Zecevic, N. (2015). Schizophrenia: A tale of two critical periods for prefrontal cortical development. Translational Psychiatry, 5(8), e623. https://doi.org/10.1038/tp.2015.115

Singer, L. T., Lewis, B. A., & Noland, J. S. (2021). Commentary: Totality of the evidence suggests prenatal cannabis exposure does not lead to cognitive impairments: A systematic and critical review. Frontiers in Psychology, 12(1). https://doi.org/10.3389/fpsyg.2021.651064

Tirado-Muñoz, J., Lopez-Rodríguez, A. B., Fonseca, F., Farré, M., Torrens, M., & Viveros, M. P. (2020). Effects of cannabis exposure in the prenatal and adolescent periods: Preclinical and clinical studies in both sexes. Frontiers in Neuroendocrinology, 57(1), 100841. https://doi.org/10.1016/j.yfrne.2020.100841

Torres, C. A., Medina-Kirchner, C., O’Malley, K. Y., & Hart, C. L. (2020). Totality of the evidence suggests prenatal cannabis exposure does not lead to cognitive impairments: A systematic and critical review. Frontiers in Psychology, 11(1). https://doi.org/10.3389/fpsyg.2020.00816

Torres, C. A., Medina-Kirchner, C., O’Malley, K. Y., & Hart, C. L. (2021). Response: Commentary: Totality of the evidence suggest prenatal cannabis exposure does not lead to cognitive impairments: A systematic and critical review. Frontiers in Psychology, 12(1), 685328. https://doi.org/10.3389/fpsyg.2021.685328

Volkow, N. D., Han, B., Compton, W. M., & McCance-Katz, E. F. (2019). Self-reported medical and nonmedical cannabis use among pregnant women in the United States. JAMA, 322(2), 167–169. https://doi.org/10.1001/jama.2019.7982

Young-Wolff, K. C., Ray, G. T., Alexeeff, S. E., Adams, S. R., Does, M. B., Ansley, D., & Avalos, L. A. (2021). Rates of prenatal cannabis use among pregnant women before and during the COVID-19 pandemic. JAMA, 326(17), 1745–1747. https://doi.org/10.1001/jama.2021.16328