Prenatal Cannabis Plus Tobacco Exposure Was Linked to Worse Behavior Problems in Children

What the researchers found

Prenatal co-exposure to cannabis and tobacco was associated with significantly greater externalizing behavior problems (aggression, rule-breaking) compared to either substance alone. Higher daily quantities of tobacco amplified the negative behavioral effects of cannabis exposure on both externalizing and internalizing scores (p<0.01). No significant interaction was found for internalizing behaviors in the main analysis.

Why it matters

Cannabis and tobacco are commonly co-used during pregnancy, but most research examines each substance in isolation. This study provides evidence that their combined prenatal effects on child behavior may be worse than either alone, which is particularly relevant as cannabis use during pregnancy rises.

The numbers in context

n=9,792 total (290 co-exposed, 225 cannabis-only, 966 tobacco-only, 8,311 unexposed); cannabis main effect p=0.03; tobacco main effect p<value; cannabis x tobacco interaction for externalizing p=0.032; dose-response interaction p<0.01 for both externalizing and internalizing.

How the study worked

Cross-sectional analysis of baseline data from the ABCD Study (children ages 9-11), comparing Childhood Behavior Checklist scores across four groups: cannabis+tobacco co-exposed (n=290), cannabis-only (n=225), tobacco-only (n=966), and unexposed controls (n=8,311), using 2x2 ANCOVA with covariate adjustment.

What this study cannot tell us

Cross-sectional baseline data cannot establish causation or developmental trajectory. Prenatal exposure is based on maternal self-report, which may underestimate true exposure. Cannot fully control for other prenatal and postnatal environmental factors that differ between exposure groups.

How to read the evidence

Moderate: Large sample from the well-designed ABCD Study, but cross-sectional analysis with self-reported exposure limits causal inference.

When this study was published

Published in 2025 using ABCD Study baseline data (children ages 9-11).

The bigger picture

This study is part of the ABCD Study, the largest long-term study of brain development in the US. The finding that co-exposure is more harmful than individual exposure supports the idea that prenatal substance interactions can compound developmental risk.

Questions still open

• Do these behavioral differences persist or change as children enter adolescence? What biological mechanisms explain the interactive effect of cannabis and tobacco? Would the findings differ with more precise exposure measurement (timing, dose, frequency)?

Common questions

Read the original research

Prenatal Cannabis and Tobacco Co-Exposure and Its Association with Behavioural Outcomes in Middle Childhood: Co-exposition prénatale au cannabis et au tabac et son association avec les résultats comportementaux au cours de l'enfance intermédiaire.

Canadian journal of psychiatry. Revue canadienne de psychiatrie, 70(1), 41-53

Citation

Nadler, Emma; Jacobus, Joanna; Rabin, Rachel A. (2025). Prenatal Cannabis and Tobacco Co-Exposure and Its Association with Behavioural Outcomes in Middle Childhood: Co-exposition prénatale au cannabis et au tabac et son association avec les résultats comportementaux au cours de l'enfance intermédiaire.. Canadian journal of psychiatry. Revue canadienne de psychiatrie, 70(1), 41-53. https://doi.org/10.1177/07067437241271696

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