The rate of pregnant people receiving emergency or hospital care related to cannabis use nearly doubled after legalization in Ontario, though absolute numbers remained small, and those visits were associated with higher rates of preterm birth and NICU admission.
Prenatal care providers, pregnant individuals, public health officials in legalization jurisdictions.
Cannabis-related pregnancy ER visits nearly doubled post-legalization; 2x odds of preterm birth
What the researchers found
The mean quarterly rate of cannabis-related acute care during pregnancy rose from 11.0 to 20.0 per 100,000 pregnancies after legalization (IRR 1.82). Mental health acute care decreased and non-cannabis substance use care did not change, serving as controls. Cannabis-related acute care during pregnancy was associated with 9.7-fold higher odds of hyperemesis gravidarum, 1.93-fold higher odds of preterm birth, and 1.94-fold higher odds of NICU admission.
Why it matters
With cannabis legalization spreading globally, understanding impacts on vulnerable populations like pregnant people is critical. While the relative increase was large, the absolute numbers remained small. The association with preterm birth and NICU stays adds urgency to prenatal screening discussions.
The numbers in context
Rate rose from 11.0 to 20.0 per 100,000 pregnancies (IRR 1.82). Post-legalization quarterly increase: 1.13 per 100,000 pregnancies. Cannabis-related visits: 9.73x odds of hyperemesis gravidarum, 1.93x odds of preterm birth (16.9% vs 7.2%), 1.94x odds of NICU admission (31.5% vs 13.0%).
How the study worked
Population-based repeated cross-sectional study in Ontario, Canada (Jan 2015-Jul 2021). Segmented regression comparing cannabis-related acute care trends to mental health and non-cannabis substance use controls. Multivariable logistic regression for neonatal outcomes.
What this study cannot tell us
Cannot determine if the increase reflects more cannabis use, more willingness to disclose, or better clinical detection. Observational design cannot establish whether cannabis caused the adverse neonatal outcomes. COVID-19 overlapped with part of the study period.
How to read the evidence
Population-based data with appropriate control conditions, though confounded by potential changes in detection and disclosure post-legalization.
When this study was published
Published 2023, using 2015-2021 data from Ontario, Canada.
The bigger picture
The gradual rather than immediate increase after legalization suggests a normalization effect: as cannabis becomes more socially acceptable, more pregnant people may use it or be more willing to disclose use. The strong link to hyperemesis gravidarum aligns with emerging research on cannabinoid hyperemesis in pregnancy.
Questions still open
- Are pregnant people using cannabis to manage pregnancy-related nausea, potentially worsening it via cannabinoid hyperemesis?
- Would targeted prenatal education about cannabis risks reduce use during pregnancy?
Common questions
Did cannabis legalization increase cannabis use during pregnancy?
Is cannabis use during pregnancy linked to birth complications?
Read the original research
Acute care related to cannabis use during pregnancy after the legalization of nonmedical cannabis in Ontario.
CMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne, 195(20), E699-E708
Citation
Myran, Daniel Thomas; Roberts, Rhiannon; Pugliese, Michael; Corsi, Daniel; Walker, Mark; El-Chaâr, Darine; Tanuseputro, Peter; Simpson, Andrea. (2023). Acute care related to cannabis use during pregnancy after the legalization of nonmedical cannabis in Ontario.. CMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne, 195(20), E699-E708. https://doi.org/10.1503/cmaj.230045
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