As breast milk contains many Cannabinoids, breastfed infants are exposed to these compounds. It has been shown that breastfed infants have higher serum concentrations of tetrahydrocannabinol (THC) than found in the mother’s blood or urine, although levels are lower than those which would produce intoxication. Studies on THC exposure through breast milk show conflicting results with some studies reporting no effect on infant behavior and others reporting subtle effects such as increased sleep duration and decreased wakefulness. This may be because there is a different concentration of THC in breast milk depending on time since last use. THC is generally considered safe for breastfed infants.
Cannabinoids naturally occurring in breast milk
Most of the psychoactive effects are due to delta-9 THC, this chemical has low acute toxicity in adults and children with a reported LD50 above 25000mg/kg body weight by ingestion or inhalation. However, some research shows that marijuana can cause immune system deficiencies which may allow respiratory infections and other infections to become more serious.
Natural cannabinoids in breast milk
There has been a recent increase in the amount of women breastfeeding their children despite using marijuana during pregnancy, some breastfeed for up to 18 month after birth. There is not enough research on how long cannabinoids can be detected in breast milk but it does seem that once usage stops there are no detectable affects on breast milk or breastfed infants.
Therefore, it can be concluded that marijuana is safe for breastfed infants as long as the mother does not use excessively and stops breastfeeding once usage ceases.