Science has long confirmed that alcohol consumed by a nursing mother makes its way into her breast milk; a finding that has prompted a range of products which ensure the safety of babies whose moms want to imbibe. But this week, a new potential concern was added to the list for new, breastfeeding moms: marijuana.
In a study published by the journal Obstetrics and Gynecology, researchers found evidence that the drug’s psychoactive component (THC) appears in breast milk hours after the drug itself is consumed. Although the study was small (just eight women), the research is the first to find proof that cannabis can be passed into breast milk—a finding that has significant implications for an infant’s health.
To investigate whether breast milk is at risk, researchers located women who considered themselves occasional marijuana users, and were currently breastfeeding an infant. After 24 hours of no marijuana, each woman was instructed to inhale a dose of 0.1 grams of cannabis, containing more than 23 percent (THC) or tetrahydrocannabinol. THC is the psychoactive ingredient in marijuana, responsible for the feeling of euphoria that the drug can sometimes yield.
After consuming the dose, the new moms collected samples of their breast milk at four different stages: 20 minutes after consuming, then one hour, two hours, and four hours. At all four points, the researchers found “low levels of THC concentrations” in the breast milk—meaning the chemical was likely passed to the infant. How much, however, is difficult to deduce.
The researchers estimated that the mean dose of THC that an infant received was 2.5 percent of their mother’s dose. This means they ingested just micrograms of the psychoactive ingredient. But the study’s authors still believe this should act as a warning. “The long-term neurobehavioral effect of exposure to delta-9-tetrahydrocannabinol on the developing brain is unclear,” the authors write. “Mothers should be cautious using cannabis during pregnancy and breastfeeding.”
Dr. Daniele Piomelli, a professor of anatomy and neurobiology at University of California Irvine, as well as director of the school’s Center for the Study of Cannabis, tells Yahoo Lifestyle that the study is “important confirmation” that THC accumulates in breast milk. Piomelli, who has spent more than two decades studying marijuana, is quick to confirm that doctors have long known about THC in breastmilk. But as to what effect it may have on the infant, he reinforces what the authors concluded: we don’t know. “Animal studies have suggested long-term effect of early life exposure to THC, but most of these studies used very high doses of THC,” he tells Yahoo Lifestyle. “We need to identify levels of exposure that pose a real risk to the mother and the offspring. That’s not easy, for a variety of ethical and experimental reasons, but it can be done and it should be done.”
So far, the main studies on THC’s effect on infants have been done on pregnant mothers. One of the most widely cited comes from the National Academy of Sciences in 2017, in which researchers concluded that THC use during pregnancy was associated with lower birth weight in infants. But that finding, which had cropped up in earlier studies, had already been disputed by contradictory evidence.
So while the science world remains in disagreement about how THC impacts an infant’s brain, a consensus seems to have been reached about whether or not it’s present in breast milk. Given this confirmation, Piomelli suggests new mothers abstain from pot. “I would recommend avoiding cannabis, alcohol, and any other drug during pregnancy and lactation,” Piomelli says. “We don’t know the consequences of exposing a developing brain to THC. I would err on the side of caution.”