Prenatal Marijuana Exposure Was Linked to Altered Brain Activity in Young Adults 18-22 Years Later
Young adults whose mothers used marijuana during pregnancy showed different brain activation patterns during executive function tasks, with consistently increased activity in left posterior brain regions despite performing tasks normally.
Quick Facts
What This Study Found
Thirty-one young adults (ages 18-22) from the Ottawa Prenatal Prospective Study, a long-running longitudinal study, underwent fMRI during four executive function tasks: visuospatial working memory, response inhibition, verbal working memory, and interference control.
Sixteen had been prenatally exposed to marijuana while 15 had not. Both groups performed the tasks equally well behaviorally, achieving similar accuracy and speed.
However, brain blood flow patterns were significantly different. The prenatally exposed group consistently showed increased activity in left posterior brain regions across all four tasks. This pattern suggests the brain may be compensating, recruiting additional neural resources to achieve the same level of task performance.
The consistency of the left posterior activation increase across four different types of executive function tasks is notable, suggesting a broad rather than task-specific alteration.
Key Numbers
31 participants aged 18-22. 16 prenatally exposed, 15 controls. Equal task performance across all 4 executive function tasks. Consistently increased left posterior brain activation in exposed group across all tasks.
How They Did This
Longitudinal cohort study from the Ottawa Prenatal Prospective Study (OPPS). 31 young adults (16 prenatally exposed, 15 controls) underwent fMRI during four executive function tasks. Prenatal marijuana exposure was documented during pregnancy through the OPPS protocols. Brain activation was compared between groups while controlling for behavioral performance.
Why This Research Matters
This is one of the longest follow-up studies of prenatal marijuana exposure, showing that brain differences are detectable 18-22 years after exposure. While the prenatally exposed individuals performed tasks normally, the altered brain activation suggests they may be working harder to achieve the same results, which could have implications for cognitive reserve and performance under stress.
The Bigger Picture
As marijuana use during pregnancy increases (some women use it for morning sickness), understanding the long-term developmental consequences is critical. This study shows that even when cognitive performance appears normal in early adulthood, the brain may be working differently, using compensatory mechanisms to maintain function.
What This Study Doesn't Tell Us
Small sample size (31 participants). The study cannot control for all postnatal environmental differences between groups. Cannabis-using mothers may have differed from non-using mothers in other ways that affected child development. The OPPS cohort used cannabis products from the 1990s, which were lower potency than current products.
Questions This Raises
- ?Would the compensatory brain activation become insufficient under higher cognitive load, revealing performance deficits?
- ?Does the altered brain pattern affect cognitive aging or resilience to neurological disease?
- ?Would higher-potency cannabis products produce more pronounced effects?
- ?Do these brain differences have real-world functional consequences?
Trust & Context
- Key Stat:
- 18-22 years after prenatal marijuana exposure, brain activation patterns were still different during executive function tasks.
- Evidence Grade:
- Moderate evidence from a unique long-term longitudinal cohort with fMRI data, though the small sample size and potential confounders limit the strength of causal conclusions.
- Study Age:
- Published in 2016 using participants from the Ottawa Prenatal Prospective Study. Modern cannabis products are significantly more potent than those used during these pregnancies.
- Original Title:
- Prenatal marijuana exposure impacts executive functioning into young adulthood: An fMRI study.
- Published In:
- Neurotoxicology and teratology, 58, 53-59 (2016)
- Authors:
- Smith, Andra M(3), Mioduszewski, Ola, Hatchard, Taylor, Byron-Alhassan, Aziza, Fall, Carley, Fried, Peter A
- Database ID:
- RTHC-01268
Evidence Hierarchy
Follows a group of people over time to track how outcomes develop.
What do these levels mean? →Frequently Asked Questions
Does prenatal marijuana exposure affect the brain long-term?
This study found that young adults whose mothers used marijuana during pregnancy showed different brain activation patterns 18-22 years later. They performed cognitive tasks normally but their brains worked differently, suggesting compensation. The long-term implications of this altered brain activity are not yet known.
If performance is normal, does it matter?
It might. Increased brain activation to achieve normal performance could mean the brain has less reserve capacity. Under high cognitive demands, stress, or with aging, this could potentially lead to difficulties that would not emerge under standard testing conditions.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-01268APA
Smith, Andra M; Mioduszewski, Ola; Hatchard, Taylor; Byron-Alhassan, Aziza; Fall, Carley; Fried, Peter A. (2016). Prenatal marijuana exposure impacts executive functioning into young adulthood: An fMRI study.. Neurotoxicology and teratology, 58, 53-59. https://doi.org/10.1016/j.ntt.2016.05.010
MLA
Smith, Andra M, et al. "Prenatal marijuana exposure impacts executive functioning into young adulthood: An fMRI study.." Neurotoxicology and teratology, 2016. https://doi.org/10.1016/j.ntt.2016.05.010
RethinkTHC
RethinkTHC Research Database. "Prenatal marijuana exposure impacts executive functioning in..." RTHC-01268. Retrieved from https://rethinkthc.com/research/smith-2016-prenatal-marijuana-exposure-impacts
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.