In-utero cannabis exposure was not associated with ADHD risk in a Quebec birth cohort | Research

The takeaway

In a cohort of 2,408 children followed up to 17 years, occasional or regular in-utero cannabis exposure was not significantly associated with the risk of developing ADHD.

Expectant parents, obstetricians, and researchers studying prenatal substance exposure effects on child development.

No significant association for occasional or regular exposure

What the researchers found

After adjusting for potential confounders, no significant association was found between in-utero cannabis exposure (occasional: OR 1.22, 95% CI 0.63-2.19; regular: OR 1.22, 95% CI 0.42-2.79) and the risk of ADHD in children.

Why it matters

Given increasing prenatal cannabis use and widespread concern about neurodevelopmental effects, this null finding from a well-designed cohort adds important nuance to the evidence base.

The numbers in context

2,408 children met inclusion criteria. 86 (3.6%) were exposed to cannabis in utero. 241 (10.0%) had ADHD diagnosis or medication. Neither occasional nor regular exposure was significantly associated with ADHD after adjustment.

How the study worked

Cohort study using the Quebec Pregnancy Cohort. Questionnaires mailed to mothers of singleton live births between 1998-2003. Cannabis exposure based on maternal self-report during pregnancy. ADHD defined by diagnosis or prescription through provincial databases. Follow-up through December 2015.

What this study cannot tell us

Cannabis exposure was self-reported by mothers and may be underreported. Relatively small number of exposed children (86). Could not account for dose, timing within pregnancy, or cannabis potency. Confounders may remain uncontrolled.

How to read the evidence

Moderate: administrative data linkage with long follow-up, but self-reported exposure and limited exposed sample.

When this study was published

Published in 2022.

The bigger picture

This finding contrasts with animal studies showing neurodevelopmental effects of prenatal THC and adds to the mixed human evidence. The question of whether prenatal cannabis exposure affects child development remains open.

Questions still open

Would larger samples or higher-potency cannabis exposure show different results? Do other neurodevelopmental outcomes (besides ADHD) show associations? Is the self-report underestimation masking a true effect?

Common questions

Does this mean cannabis is safe during pregnancy?

This study only examined one outcome (ADHD) and found no association. It does not address other potential risks of prenatal cannabis use, and the small number of exposed children limits statistical power.

How was ADHD measured?

ADHD was identified through provincial health databases using either a medical diagnosis code or a prescription filled for ADHD medication, providing objective rather than self-reported outcome data.

How long were children followed?

Children born between 1998-2003 were followed through December 2015, allowing up to 17 years of follow-up to capture ADHD diagnoses that may emerge at school age.

Read the original research

Is in-utero exposure to cannabis associated with the risk of attention deficit with or without hyperactivity disorder? A cohort study within the Quebec Pregnancy Cohort.

BMJ open, 12(8), e052220

View on PubMed ↗Publisher’s paper ↗

Citation

Tchuente, Vanina; Sheehy, Odile; Zhao, Jin-Ping; Gorgui, Jessica; Gomez, Yessica-Haydee; Berard, Anick. (2022). Is in-utero exposure to cannabis associated with the risk of attention deficit with or without hyperactivity disorder? A cohort study within the Quebec Pregnancy Cohort.. BMJ open, 12(8), e052220. https://doi.org/10.1136/bmjopen-2021-052220