Association of Preconception and Prenatal Cannabis Use with Breastfeeding.

Introduction: Breastfeeding is recommended. It is unknown whether preconception or prenatal cannabis use are related to breastfeeding behaviors.

Methods: This population-based retrospective cohort study included 200,207 pregnancies in Northern California (2016-2022) with live births screened in early pregnancy for cannabis use. Exposures included prenatal cannabis use, preconception cannabis use only, or no cannabis use. Additional analyses considered frequency of prenatal cannabis use. Longitudinal breastfeeding outcomes assessed at each well-child visit during the first year included any breastfeeding, and full breastfeeding (breastmilk without formula). Adjusted prevalence ratios (aPRs) were calculated using modified Poisson regression for longitudinal binary outcomes in 2024 and 2025. The risk of stopping breastfeeding among those who started was modeled using Cox proportional hazard regression.

Results: Overall, 7.6% of pregnancies had preconception cannabis use only and 7.2% had prenatal use. Most people (94.6% overall) initiated breastfeeding, with only modest differences by cannabis use (94.9% no cannabis use, 95.7% preconception cannabis use only, 90.5% prenatal cannabis use). However, over time, prenatal cannabis use was associated with earlier discontinuation of breastfeeding (aHR 1.12, 95% CI: 1.09-1.15) and lower prevalence of breastfeeding (aPR 0.84, 95% CI: 0.82-0.85 at 6 months, aPR 0.81, 95%CI: 0.78-0.83 at 12 months). Associations were stronger for higher frequency use. There were small differences in breastfeeding among those with preconception cannabis use only verses none. Full breastfeeding results were similar.

Conclusions: Despite high prevalence of breastfeeding initiation, prenatal cannabis use was associated with earlier breastfeeding discontinuation and lower prevalence at 6 and 12 months.