Late Prenatal THC Exposure Tied to Attention Problems, ADHD and Developmental Problems

Prenatal exposure to delta 9-tetrahydrocannabinol (Δ9-THC) detected at delivery was associated with higher scores for attention problems, attention deficit hyperactivity disorder (ADHD) symptoms, and pervasive developmental problems at age 5 years, according to a cohort study published in The Journal of Pediatrics.

The authors noted that cannabis has surpassed tobacco as the most commonly used substance during pregnancy. To identify critical windows of exposure, they measured Δ9-THC and its metabolites in maternal serum at about 17 and 27 weeks' gestation and in umbilical cord blood at delivery, rather than relying on self-report. Behavior was assessed with the Child Behavior Checklist (CBCL) and cognition with the NIH Toolbox.

The analysis included 460 mother-child pairs from the Healthy Start study, a racially and ethnically diverse Colorado cohort. Δ9-THC exposure prevalence was 8% at 17 weeks, 6% at 27 weeks, and 5% at delivery. Compared with no exposure at delivery, exposure at delivery was associated with higher T-scores for attention problems, ADHD symptoms, and pervasive developmental problems. Associations with these outcomes and with externalizing behaviors varied by exposure timing, with generally stronger signals at delivery.

In the primary analysis, exposure was not associated with cognitive flexibility, inhibitory control, or receptive language. The authors noted that adjusted mean CBCL T-scores among exposed children remained below clinical thresholds for further evaluation. They wrote that the findings suggest "it is never too late to quit" cannabis use during pregnancy to limit adverse effects on child neurodevelopment.

The authors cited possible residual confounding, as exposed mothers tended to be younger, have lower household income and education, and report more tobacco use. They could not account for substance use other than tobacco or alcohol, and behavior was parent-reported. Twelve children were classified as exposed at delivery, and the authors said the small number of exposed participants limited dose-response analyses.

Source: Moore BF, Crume T, Wilkening G, et al. Prenatal exposure to delta 9-tetrahydrocannabinol and child neurodevelopment: a critical windows analysis. J Pediatr. Published online October 15, 2026. doi:10.1016/j.jpeds.2026.115363