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.
P.S. If you, like me, find yourself eagerly awaiting the next episode of Vanderpump Rules, look no further than the scientific, yet surprisingly spirited, exchange between Torres et al. (2020, 2021) and Singer et al. (2021). The open-access trades over methodology and interpretation prove scientists are just like us—prone to squabbles, if decidedly more highbrow.
Vector illustration of two elderly scientists or doctors having a heated debate. From iStock.com. Credit: kbeis. Modified using iStock Editor.
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2 thoughts on “Cannabis in the Womb: Separating Smoke from Science”
I’m so glad my friend sent me this article. It is something I have always been interested about and wanted to look into, so thank you for writing about the current standings of research on the topic!
I had not given much thought to the effect of weed while pregnant! I think this is an important topic of research, and mimics some of the ambigious effects of cannabis intoxication while driving. However, I agree it is better safe then sorry. It seems that almost the 3.5 year olds cognitive functioning was not impaired from cannabis exposure in the womb, but 6 year olds was, is this implying that impaired cognitive abilities may develop later in life/age then immediately after? Another interesting but important thing to note.