The Grapevine

Marijuana Remains In Breast Milk Till Nearly Week After Mother's Last Use

Mothers who use marijuana may also have traces of the drug in their breast milk. Researchers at the University of California (UC), San Diego could find small amounts of the primary psychoactive ingredient nearly a week after their last reported use.

The findings of the study were published in the journal Pediatrics on Aug. 27.

"Pediatricians are often put into a challenging situation when a breastfeeding mother asks about the safety of marijuana use," said Dr. Christina Chambers, principal investigator of the study and professor in the Department of Pediatrics at UC San Diego School of Medicine. "We don't have strong, published data to support advising against use of marijuana while breastfeeding, and if women feel they have to choose, we run the risk of them deciding to stop breastfeeding — something we know is hugely beneficial for both mom and baby."

It is generally recommended that exclusive breastfeeding take place for the first six months, as the milk provides essential nutrients to the infant. It also contains antibodies to help reduce the risk of infections and illnesses for the baby. As for the mother, studies have found an association between breastfeeding and a reduced risk of breast cancer, uterine cancer, and type 2 diabetes.

The research team recruited 50 female marijuana users who smoked every day, every week, or sporadically. After examining 54 samples of breast milk from the women, they detected small amounts of tetrahydrocannabinol or THC.

THC is the main psychoactive ingredient in marijuana which causes the "high," experienced by users. The team was able to find traces of the ingredient in 34 of 54 samples up to six days after the last reported use of marijuana by the mother.

Another recent study followed children from infancy till the age of 11 to determine whether alcohol consumption by breastfeeding mothers was safe. Unlike marijuana, the researchers noted that waiting a few hours after drinking was enough to reduce the risk of exposure. 

It is believed that active compounds in marijuana have a tendency to bind to fat molecules, which breast milk contains in large quantities. This may explain why traces of THC have been able to stick around even after a relatively long period without use.

The American Academy of Pediatrics strongly advises breastfeeding mothers to avoid marijuana. Experts have had concerns about negative effects on the vulnerable infant brain, especially if there was a chance of irreversible damage in the areas related to learning and memory.

But overall, there is still a dearth of evidence on how exactly exposure to THC can affect on-going or future development.

"We found that the amount of THC that the infant could potentially ingest from breast milk was relatively low, but we still don't know enough about the drug to say whether or not there is a concern for the infant at any dose, or if there is a safe dosing level," Chambers said. "The ingredients in marijuana products that are available today are thought to be much more potent than products available 20 or 30 years ago."