Separate from the direct, chemical effects of marijuana on a baby, use of marijuana may affect a mother's ability to be able to properly care for her baby. Maternal judgment may be impaired.
Any secondhand smoke the baby is exposed to increases the amount of the drug your baby receives. Also, because street drugs are rarely pure, marijuana may be laced with other drugs or substances that can also be harmful to the breastfeeding baby.
The active ingredient in marijuana, THC, will be stored in mom's fat tissues for long periods (weeks to months) and will build up in the body with continued use. Small to moderate secretion into breastmilk has been documented, and THC is concentrated in human milk. According to Hale, analysis of breastmilk from chronic heavy users indicated an eight-fold concentration in milk compared to mom's blood plasma, however the dose received by baby was insufficient to produce significant side effects. Studies have shown significant absorption and metabolism in infants, although long term effects have not been shown.