Marijuana should not be used by nursing mothers because it may impair their judgment and child care abilities. Marijuana should not be smoked by anyone in the vicinity of infants because the infants may be exposed by inhaling the smoke. Some evidence indicates that paternal marijuana use increases the risk of sudden infant death syndrome in breastfed infants.
Although published data are old and limited, it appears that active components of marijuana are excreted into breastmilk in small quantities. Data are from random breastmilk screening rather than controlled studies because of ethical considerations in administering marijuana to nursing mothers. Concern has been expressed regarding marijuana's possible effects on neurotransmitters, nervous system development and endocannabinoid-related functions. One long-term study found that daily or near daily use might retard the breastfed infant's motor development, but not growth or intellectual development. This and another study found that occasional maternal marijuana 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 marijuana can affect serum prolactin variably, it appears not to adversely affect the duration of lactation.
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.
The main active component of marijuana is delta-9-tetrahydrocannabinol (THC), although it also contains other active compounds. THC is very fat soluble and persistent in the body fat of users and slowly released over days to weeks, depending on the extent of use.
Two women who smoked marijuana daily while nursing had their randomly collected milk analyzed. One mother who reported smoking marijuana once daily had a milk tetrahydrocannabinol concentration of 105 mcg/L; other metabolites were absent. The second mother who reported smoking marijuana 7 to 8 times daily had a milk THC concentration of 340 mcg/L; the metabolite 11-hydroxy-THC was found in a concentration of 4 mcg/L and 9-carboxy-THC was absent. A milk sample that was collected 1 hour after smoking marijuana contained 60.3 mcg/L of THC, 1.1 mcg/L of 11-hydroxy-THC and 1.6 mcg/L of 9-carboxy-THC. One source used data in this study to estimate that the infant receives about 0.8% of the maternal weight-adjusted dosage.
A woman who admitted to smoking cannabis (amount not stated) donated milk for analysis. THC was present in a concentration of 86 mcg/L and 11-hydroxy-THC was present in a concentration of 5 mcg/L; 11-nor-carboxy-9-tetrahydrocannabinol was not detected.
Breastmilk from a mother who admitted to cannabis use contained THC in a concentration of 86 mcg/L and 11-hydroxy-THC in a concentration of 5 mcg/L. The time of collection and amount of drug use was not stated.
The urine of 2 breastfed infants whose mothers smoked marijuana found none of the 9-carboxy-THC metabolite. One mother reported smoking marijuana once daily and the other reported smoking marijuana 7 to 8 times daily. Analysis of the feces of the latter mother's infant revealed a higher proportion of metabolites than THC, indicating that THC was probably absorbed from the milk, metabolized by the infant, and excreted in feces.
Effects in Breastfed Infants:
Sixty-two infants whose mothers reported smoking marijuana during breastfeeding were compared at 1 year of age to the infants of mothers who smoked marijuana during pregnancy but not during breastfeeding. No differences were found in growth, or on mental and motor development.
Sixty-eight infants whose mothers reported smoking marijuana during breastfeeding were compared to 68 matched control infants whose mothers did not smoke marijuana. The duration of breastfeeding varied, but the majority of infants were breastfeed for 3 months and received less than 16 fluid ounces of formula daily. Motor development of the marijuana-exposed infants was slightly reduced in a dose-dependent (i.e., number of reported joints per week) manner at 1 year of age, especially among those who reported smoking marijuana on more than 15 days/month during the first month of lactation. No effect was found on mental development.
A small, case-control study found that paternal marijuana smoking postpartum increased the risk of sudden infant death syndrome. In this study, too few nursing mothers smoked marijuana to form any conclusion.
A study of women taking buprenorphine for opiate substitution during pregnancy and lactation found that 4 of the women were also using cannabis as evidenced by positive urine screens for THC between 29 and 56 days postpartum. One was also taking unprescribed benzodiazepines. One infant was exclusively breastfed and the other 3 were mostly breastfeeding with partial supplementation. Infants had no apparent drug-related adverse effects and showed satisfactory developmental progress.
Possible Effects on Lactation:
Acute one-time marijuana smoking suppresses serum concentrations of luteinizing hormone and prolactin in nonpregnant, nonlactating women. However, hyperprolactinemia has been reported in chronic marijuana users, and galactorrhea and hyperprolactinemia were reported in a woman who smoked marijuana for over 1 year. The prolactin level in a mother with established lactation may not affect her ability to breastfeed.
Of 258 mothers who reported smoking marijuana during pregnancy, 62 who had smoked marijuana during breastfeeding were followed-up at 1 year. No difference was found in the age of weaning between these mothers and those who reported not smoking marijuana during breastfeeding.
A prospective study in a Canadian, middle-class population found no effect of maternal marijuana use during lactation and the duration of breastfeeding.
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