• Posted May 9, 2024

How Long Does Marijuana THC Linger in Breast Milk?

New mothers who like to smoke marijuana might wind up exposing their babies to THC through their own breast milk, a new study says.

THC, the intoxicating compound in cannabis, dissolves in the fats contained in human milk, researchers found.

Mother's milk produced by weed users always had detectable amounts of THC, even when the mothers had abstained for 12 hours, results show.

The amounts detected were low"infants receive an average of 0.07 milligrams of THC per day through breast milk, researchers estimate. By comparison, a common low-dose edible contains 2 milligrams of THC.

However, researchers emphasize that no one knows how any amount of THC might affect an infant or its development.

"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,"lead researcher Courtney Meehan, a biological anthropologist at Washington State University, said in a news release.

Worse, there's no consistent time when a weed user can expect the THC concentrations in their breast milk to peak and then decline.

Guidelines for new mothers say to wait at least two hours after drinking alcohol before breastfeeding. There are no similar guidelines for cannabis.

For participants who used cannabis just once during the study, THC in breast milk peaked between 30 minutes and 2.5 hours after use before declining.

Moms who used weed more often during the study showed a continual increase in THC concentrations throughout the day.

"There was such a range. 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,"said lead researcher Elizabeth Holdsworth. She worked on the study while doing post-doctoral work at Washington State University and is now an assistant professor of anthropology at Ohio State University.

For the study, researchers analyzed milk from 20 breastfeeding mothers who use cannabis, all with infants younger than 6 months.

The moms provided detailed reports on their weed use, and collected milk samples after abstaining from cannabis for at least 12 hours and then at regular intervals after use.

The samples were all taken in their homes at times of their own choosing, with weed they purchased themselves.

An earlier study by the same team found that many breastfeeding moms use weed for therapeutic purposes"to manage anxiety or deal with chronic pain, for example.

"Our results suggest that mothers who use cannabis are being thoughtful in their decisions,"researcher Shelley McGuire, a University of Idaho professor who studies maternal-infant nutrition, said. "These women were mindful about their choices. This is far from a random lifestyle choice."

The researchers noted that THC is only one of a number of commonly used substances that can be found in breast milk, for which almost nothing is known concerning the effect on breastfeeding babies.

"This is an area that needs substantial, rigorous research for moms to know what's best,"McGuire said.

The new study appears in the journal Breastfeeding Medicine.

More information

The U.S. Centers for Disease Control and Prevention has more on weed during breastfeeding.

SOURCE: Washington State University, news release, May 8, 2024