In the study, 50 women who reported using cannabis supplied breast milk samples to Mommy’s Milk, a human milk research lab at the University of California, San Diego. The women also filled out a questionnaire with information about the use of cannabis and other medications during the 14 days prior to giving the samples.
Analysis of the samples showed the presence of THC in 34, or 63 percent, of the 54 samples. Five of the samples, or 9 percent, had detectable levels of CBD. THC was detected in samples up to six days after reported cannabis use.
Christina Chambers is a professor of pediatrics at UCSD, the director of clinical research for the Department of Pediatrics at UCSD and Rady Children’s Hospital in San Diego and one of the study’s senior authors. She said that the effect the cannabinoids may have on a developing fetus has not been determined.
“Whether this means that some level—or any level—of these metabolites can negatively influence child development is unknown at this point,” Chambers said.
“It’s important to be able to know the answers to those questions so the advice that pediatricians and obstetricians are giving to pregnant women and breastfeeding women are based on sound evidence. This is a call to action to take the next steps to study long-term outcomes in these children,” she added.
Chambers noted that the presence of THC in breast milk does not necessarily mean that children will be affected by the cannabinoid.
“The question is, does it matter? … Is it possible that even low levels in breast milk may have an effect on a child’s neurodevelopment? And we don’t know the answer to that,” she said.
Dr. Melissa Bartick, an assistant professor of medicine at Cambridge Health Alliance and Harvard Medical School in Massachusetts who did not participate in the study, said that researchers don’t know if THC in breast milk can be absorbed by nursing children.
“To look at that, we’d first have to see if levels in the milk translate into levels in the infants’ blood,” Bartick said.
“We would have to measure any cognitive, intellectual, and behavioral effects on the children as related to blood levels, while eliminating confounding factors such as exposure during pregnancy and the effects of parenting while under the influence,” she added. “So there is little we can advise from this study except more research.”
Chambers said that her team is planning further work to study the effect that THC exposure in children can have on their performance in neurobehavioral testing.
“That’s a testable hypothesis and something that we want to move forward with trying to answer because it’s a critical question,” Chambers said.
Until more research can be performed, the study’s authors suggest that nursing mothers follow current recommendations from medical experts.
“Lacking definitive data on the risk or safety of infant exposure to cannabis through breast milk, the American Academy of Pediatrics and the American Congress of Obstetricians and Gynecologists advise that marijuana use should be discouraged while breastfeeding,” the report reads.