A nursing mother uses marijuana. What happens?

When a nursing mother uses marijuana, some of the marijuana's THC is passed to the baby in her breast milk. This is a matter for concern, since the marijuana's THC in the mother's milk is much more concentrated than that in the mother's blood. One study has shown that the use of marijuana by a mother during the first month of breastfeeding can impair the infant's motor development (control of muscle movement). This work has not been replicated, although similar anecdotal reports exist. Further research is needed to determine whether marijuana's THC transmitted in breast milk has harmful effects on development.