Study: Occasional Prenatal Marijuana Exposure Not Linked to Worse Cognitive Development in Adolescence After Adjusting for Social Factors

A new study published in Alcohol, Clinical & Experimental Research found that occasional prenatal marijuana exposure was not associated with worse cognitive development during adolescence once researchers accounted for socioeconomic and demographic factors.

The study was conducted by researchers from the University of Michigan, Medical University of South Carolina and University of Sydney. It used data from 11,029 participants in the Adolescent Brain Cognitive Development Study, tracking cognitive performance at roughly ages 10, 12 and 14.

Researchers examined how prenatal marijuana exposure affected performance over time in five areas: attention, reading, processing speed, memory and vocabulary. Before adjusting for outside factors, prenatal marijuana exposure appeared linked to lower baseline scores across all five domains. But after researchers controlled for variables such as household income, parental education, race, birthweight and parental history of substance issues, those associations were no longer statistically significant.

The researchers also looked at how often marijuana was used during pregnancy and reached the same general conclusion. More frequent prenatal marijuana exposure appeared tied to lower scores at first, but those findings disappeared after the same adjustments were made. In other words, the study found little evidence that low-level prenatal marijuana exposure had an independent effect on cognitive development during adolescence.

The researchers say this is important because marijuana use during pregnancy is often studied alongside many other social and economic variables that can strongly influence childhood development. In this study, children exposed to marijuana in the womb were more likely to come from households with lower income and lower parental education, both of which were also associated with lower cognitive scores.

The study also found no evidence that combined low-level exposure to both marijuana and alcohol during pregnancy had a measurable effect on adolescent cognitive trajectories.

Researchers caution that the findings apply only to occasional exposure in a general population sample (an average of 33 “cannabis sessions” per pregnancy), not heavy use. They also note that marijuana potency has increased in recent years, meaning newer patterns of use may not be fully reflected in the data.

Still, the study adds to a growing body of research indicating that low-level prenatal marijuana exposure may not by itself predict poorer long-term cognitive outcomes once broader life circumstances are taken into account.