Maternal Cannabis Use and Secretory IgA and IgM Concentrations in Breast Milk

Breast milk is the gold standard for infant nutrition, providing essential nutrients and bioactive factors such as secretory immunoglobulins A (SIgA) and M (SIgM). The association between maternal cannabis consumption and SIgA and SIgM concentrations in breast milk remains poorly understood, despite the rising trends in cannabis consumption among women of reproductive age.

To examine the association between maternal characteristics and cannabis use patterns and SIgA and SIgM concentrations in breast milk.

This prospective cohort study enrolled 160 pregnant and lactating women (110 controls and 50 cannabis users) between January 2023 and December 2024. Mature breast milk samples were collected 4-16 weeks postpartum and analyzed for five cannabinoids (Δ⁹-tetrahydrocannabinol, 11-nor-9-carboxy-Δ⁹-tetrahydrocannabinol, 11-hydroxy-Δ⁹-tetrahydrocannabinol, cannabinol, and cannabidiol) followed by SIgA and SIgM quantification. Participants provided sociodemographic, pregnancy, and cannabis use characteristics via questionnaire.

Cannabis consumers were younger, had lower levels of education, and higher parity than nonusers (all p < 0.01). Increasing maternal age was associated with lower SIgA and SIgM levels (both p < 0.05). SIgA was higher among participants who consumed both cannabis and nicotine compared with controls (1.27 versus 0.60 g/L; p = 0.002), whereas participants who consumed cannabis alone did not differ significantly (p = 0.094).

Maternal age was the characteristic most consistently associated with breast milk immunoglobulin concentrations, with older age associated with lower SIgA and SIgM. Higher SIgA observed among participants using both cannabis and nicotine was substantially accounted for by concurrent nicotine use. The clinical significance of these small differences remains unknown, and larger studies able to separate cannabis from co-occurring substance use are needed.