Effects of Marijuana on the Fetus and Breastfeeding Infants.

Cannabis has enormous affinity for milk and produces a milk/plasma ratio of 8, although the levels in milk are generally considered subclinical. THC crosses the placenta readily, and there is increasing evidence that it may increase rates of growth retardation and adverse neurodevelopment following prenatal exposure.
 
One study indicated an increased incidence of reduced head circumference in young adolescents (9-12 years of age) who were exposed in utero to heavy marijuana use.  Prenatal exposure resulted in a higher rate of low birth weight infants and childhood leukemia. Recent studies have suggested a reduction in long and short-term memory retrieval and retention in children exposed to prenatal cannabis. These children were also weak in planning, integration, and judgment skills.
 
While the effect of cannabis on infants from breastfeeding mothers is limited, cannabis use in breastfeeding mothers should be strongly discouraged. Thus, in pregnant and breastfeeding mothers, this drug should no longer be viewed as safe.