With recent legalization of marijuana in numerous U.S. states, the risk of marijuana exposure via breast milk is a rising concern. This review analyzes the available human and animal literature regarding maternal use of marijuana during lactation. The findings can be categorized into four areas of analysis: effects of marijuana on the mother, transfer into milk, transfer to the offspring, and effects on the offspring. Human and animal data have reported decreased prolactin levels as well as potential maternal psychological changes. Animal and human studies have reported transfer into milk; levels were detected in animal offspring, and metabolites were excreted by both human and animal offspring. Further, animal data have predominately displayed motor, neurobehavioral, and developmental effects, whereas human data suggested possible psychomotor outcomes; however, some studies reported no effect. Despite these results, many human studies were marred by limitations, including small sample sizes and confounding variables. Also, the applicability of animal data to the human population is questionable and the true risk of adverse effects is not entirely known. There are large gaps in the literature that need to be addressed; in particular, studies need to focus on evaluating the short- and long-term consequences of maternal marijuana use for the infant and the potential for different risks based on the frequency of maternal use. Until further evidence becomes available, practitioners need to weigh the benefits of breastfeeding for mother and child, with the potential influence of marijuana on infant development when determining the infant's most suitable form of nutrition.
Keywords: THC; breastfeeding; cannabis; infant exposure; lactation; marijuana.