How long does marijuana THC linger in breast milk for new moms? What new study found
Cannabis is one of the most widely used substances among Americans, officials say, and some studies suggest it is safer than alcohol or other drugs.
It is also one of the most commonly used drugs during breastfeeding, experts say. New mothers dealing with pain or anxiety may be more inclined to reach for cannabis over other options, according to research.
However, a new study out of Washington State University found that cannabis use while breastfeeding may have some unintended consequences.
Breastfeeding mothers who use cannabis may be transferring THC to their babies, researchers found. The study, published May 2 in the journal Breastfeeding Medicine found that THC, the psychoactive compound in cannabis — the thing that makes a person feel “high” — lingers in breast milk many hours after cannabis use.
“Breastfeeding parents need to be aware that if they use cannabis, their infants are likely consuming cannabinoids via the milk they produce, and we do not know whether this has any effect on the developing infant,” researcher Courtney Meehan said in a May 8 news release.
Meehan and her colleagues analyzed the breast milk of 20 women at different intervals following cannabis use.
The sample size in the study was small, a limitation the scientists acknowledge in the paper. Studies on pregnant and breastfeeding individuals are not often done due to both ethical and safety concerns, according to the National Institutes of Health. This particular investigation found participants who were already cannabis users, as opposed to introducing cannabis to new parents who weren’t already using it.
Researchers found the breast milk of the participants consistently had detectable amounts of THC, even when the users had not used cannabis for 12 hours.
The reason for this, according to Meehan, is due to the composition of breast milk as well as how cannabis behaves in the body.
“Human milk has compounds called lipids, and cannabinoids are lipophilic, meaning they dissolve in those lipids. This may mean that cannabinoids like THC tend to accumulate in milk — and potentially in infants who drink it,” said Meehan.
The study also found that cannabis levels in breast milk were hard to predict. Participants who used cannabis only one time during the study saw breast milk THC levels peak approximately 30 minutes to 2½ hours after use before starting to decline.
Conversely, participants who used cannabis multiple times showed steadily increasing THC concentrations throughout the day. For mothers trying to use cannabis mindfully while juggling a breastfeeding schedule for their infant, this is not great news, according to researchers.
“If you’re trying to avoid breastfeeding when the concentration of THC peaks, you’re not going to know when THC is at its peak in the milk,” Elizabeth Holdsworth, another researcher in the study, said in the release.
New parents trying to manage their own well-being alongside their infant’s health might want to proceed cautiously when it comes to cannabis use, scientists say. While THC levels in breast milk were low, its persistence in the milk is cause for prudence, researchers say.
According to the study, scientists don’t yet know how even small amounts of THC could affect infants. Smoking marijuana is not recommended for children whose brains are still developing, according to a 2023 study published in the journal Frontiers for Young Minds.
Michelle McGuire, another researcher in the new study, hopes to see science pursue the answer to this question.
“This is an area that needs substantial, rigorous research for moms to know what’s best,” she said in the release.
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