The main psychoactive component of cannabis, tetrahydrocannabinol (THC), is excreted into breastmilk in small quantities. The duration of detection of THC in milk has ranged from 6 days to greater than 6 weeks in various studies. A pharmacokinetic model predicted a half-life in milk of 39 hours which is consistent with a THC clearance from milk in about 8 days. Concern has been expressed regarding the possible effects of cannabis on neurotransmitters, nervous system development and endocannabinoid-related functions.[1,2] One preliminary study found a decrease in secretory IgA (SIgA) levels in the milk of cannabis users.[3] A 1-year study found that daily or near daily use might retard the breastfed infant's motor development, but not growth or intellectual development.[4] This and another study[5] found that occasional maternal cannabis use during breastfeeding did not have any discernable effects on breastfed infants, but the studies were inadequate to rule out all long-term harm. Although cannabis can affect serum prolactin variably, it appears not to adversely affect the duration of lactation. However, maternal perception that their use of cannabis is harmful to their infants are likely to discontinue breastfeeding earlier than mothers who do not believe it is harmful.[6] Other factors to consider are the possibility of positive urine tests in breastfed infants, which might have legal implications, and the possibility of other harmful contaminants in street drugs.
Because of insufficient long-term data on the outcome of infants exposed to cannabis via breastmilk, health professionals' opinions on the acceptability of breastfeeding by cannabis-using mothers varies. In general, professional guidelines recommend that cannabis use should be avoided by nursing mothers, and nursing mothers should be informed of possible adverse effects on infant development from exposure to cannabis compounds in breastmilk. In addition to possible adverse effects from cannabinoids in breastmilk, paternal cannabis use may also increase the risk of sudden infant death syndrome in breastfed infants. Cannabis should not be smoked by anyone in the vicinity of infants because the infants may be exposed by inhaling the smoke.[7-10]