Systematic review found no clear link between prenatal cannabis and child cognitive outcomes | Research

The takeaway

A systematic review of 28 studies covering over 500,000 patients found no significant pooled associations between prenatal cannabis exposure and offspring intelligence, attention, reading, or math scores.

Prenatal care providers, developmental psychologists, parents, and researchers studying prenatal substance exposure effects.

28 studies, 523,107 patients; no significant pooled cognitive associations

What the researchers found

Meta-analyses showed no significant associations between prenatal cannabis exposure and attention, global IQ, reading, written comprehension, spelling, or mathematics. Individual studies of heavy use showed some differences, but these disappeared when outcomes were pooled.

Why it matters

Prenatal cannabis exposure is increasing and parents need evidence about risks. This comprehensive review suggests the cognitive effects, if any, may be smaller than commonly assumed, though evidence quality is low.

The numbers in context

28 studies, 523,107 total patients. Pooled standardized mean differences (all non-significant): attention -0.27, IQ -0.16, reading -0.05, written comprehension -0.09, spelling -0.04, mathematics -0.01. Evidence graded as very low quality.

How the study worked

Systematic review with meta-analyses following standard guidelines. Searched MEDLINE, EMBASE, PsychINFO, CINAHL, and ClinicalTrials.gov. 28 studies included (n=523,107 patients). Random-effects models used when at least three studies reported the same outcome. GRADE assessment applied.

What this study cannot tell us

Very low-quality evidence by GRADE assessment. Significant heterogeneity across studies. Cohort redundancy (multiple papers from the same cohorts) limited meta-analysis. Heavy use subgroups showed effects that disappeared when pooled. Self-reported exposure likely misclassified many participants.

How to read the evidence

Systematic review with meta-analyses, but underlying evidence graded as very low quality due to heterogeneity, confounding, and measurement issues.

When this study was published

Published 2023.

The bigger picture

The prenatal cannabis literature is plagued by confounding, cohort overlap, and inconsistent exposure measurement. This null pooled finding does not prove safety but suggests that if cognitive effects exist, they are small and inconsistent across studies.

Questions still open

Are there dose-dependent cognitive effects that only emerge with heavy use? Would studies using biomarker-verified exposure and longer follow-up reveal effects masked in current research?

Common questions

Does prenatal cannabis exposure affect children's intelligence?

This large systematic review found no significant pooled associations between prenatal cannabis exposure and children's IQ, attention, reading, or math scores across 28 studies. However, the evidence quality was very low, and some individual studies of heavy use showed effects. The absence of a clear association does not prove cannabis is safe during pregnancy.

Why is the evidence quality so low?

Multiple factors degrade evidence quality: studies used different definitions of cannabis exposure, many relied on self-report which underestimates use, overlapping cohorts inflated the apparent number of independent studies, and it is difficult to separate cannabis effects from co-occurring tobacco, alcohol, and socioeconomic factors.

Read the original research

Prenatal cannabis use and its impact on offspring neuro-behavioural outcomes: A systematic review.

Paediatrics & child health, 28(1), 8-16

View on PubMed ↗Publisher’s paper ↗

Citation

Thompson, Mary; Vila, Merima; Wang, Li; Thabane, Lehana; Shea, Alison K. (2023). Prenatal cannabis use and its impact on offspring neuro-behavioural outcomes: A systematic review.. Paediatrics & child health, 28(1), 8-16. https://doi.org/10.1093/pch/pxac079