What cannabis use may—and may not—change in breastmilk

Human milk is a dynamic biofluid influenced by maternal health, diet, and environmental exposures, including cannabis consumption. To synthesize current evidence on whether maternal cannabis consumption is directly associated with alterations in the macronutrient and immunological composition of breastmilk, and to identify dietary patterns and social adversity as key confounding variables requiring methodological consideration in future research. A narrative review of the peer-reviewed literature was conducted. Relevant studies were identified using selected keywords searched individually and in combination. Search was not restricted by date but prioritized recent literature, with seminal studies included where relevant. Studies were selected based on relevance to the review questions; no formal inclusion or exclusion criteria were applied, consistent with the narrative review methodology. Maternal diet is a key determinant of breastmilk composition, particularly for fatty acids. Emerging evidence suggests that cannabis consumption may be associated with alterations in fat and protein concentrations, and may affect immune components such as Secretory Immunoglobulin A (SIgA). However, these associations may be confounded by cannabis-related changes in dietary patterns and by socioeconomic disadvantages that influence maternal nutrition and health. Findings remain limited and inconsistent, and underlying biological mechanisms remain poorly understood. Current evidence on the impact of maternal cannabis use on breastmilk composition is sparse and inconclusive. Further research is needed to disentangle the direct effects of cannabis exposure from related dietary and social determinants to clarify implications for infant growth, immune development, and long-term health outcomes.