Back in 2018, the American Academy of Pediatrics (AAP) issued a warning urging mothers not to use cannabis while breastfeeding. This warning was based on the findings of a research study suggesting that THC can remain in breast milk for as long as six days after consumption of cannabis, and this cannabinoid can be passed from mother to infant.
Now, a new study in the JAMA Pediatrics journal is reporting that THC can be found in breast milk for as long as six weeks after use, not just six days. Researchers from the Children's Hospital Colorado studied 25 women who gave birth at two Colorado hospitals between November 2016 and June 2019. All of these women had used weed at some point during their pregnancy and intended to breastfeed their children.
Now that most US states have legalized medical marijuana, more and more women are using cannabis to help them with nausea, pain, sleep, and other issues. A 2019 study found that the rate of prenatal cannabis use has doubled in the past 15 years, and a 2018 study found that 70 percent of Colorado dispensaries recommended weed to expecting mothers. But other than the AAP study, there has been little research into exactly how long cannabinoids can remain in breast milk.
“With the increasing utilization of marijuana in society as a whole, we are seeing more mothers who use marijuana during pregnancy,” said Children’s Colorado neonatologist Erica Wymore, MD, MPH in a statement. “However, given the lack of scientific data regarding how long THC persists in breast milk, it was challenging to provide mothers with a definitive answer regarding the safety of using marijuana while breastfeeding and simply ‘pumping and dumping’ until THC was no longer detectable in their milk. With this study, we aimed to better understand this question by determining the amount and duration of THC excretion in breast milk among women with known prenatal marijuana use.”
For this new study, researchers asked each subject to abstain from cannabis for six weeks after giving birth, and seven women completely quit weed during the full duration of the study. Throughout the course of the study, researchers collected blood, urine, and breast milk samples from each subject.
The study reports that THC was present in every single mother’s breast milk for as long as six weeks after they last used cannabis. The exact concentration of THC in each sample of breast milk was different, likely due to each woman's unique metabolism, weight, and the amount of pot they used.
The findings of this study are limited by the extremely small study size and the fact that researchers only looked at women from two hospitals in one state, so further research is necessary to expand upon these findings.
“This study provided invaluable insight into the length of time it takes a woman to metabolize the THC in her body after birth, but it also helped us understand why mothers use marijuana in the first place,” explained Maya Bunik, MD, MPH, medical director of the Child Health Clinic and the Breastfeeding Management Clinic at Children’s Colorado.
Researchers now know that a growing number of pregnant women are using pot to help them cope with nausea and other issues, and that THC from this weed can be passed on to children via breast milk. What is not yet clear, though, is how these small doses of THC can actually affect newborns.
Studies from the 1980s reported that children born to cannabis-using mothers experienced long-term cognitive deficits, but more recent research has found absolutely no evidence linking prenatal weed use with cognitive impairments. Other studies have found that THC could interfere with the development of neural connections in the growing brain, but it is unclear if the small amount of THC transferred through breast milk could cause these issues.
Researchers are still working to create a definitive picture of exactly how prenatal cannabis use might impact children, but until that research has matured, medical professionals continue to advise women to abstain from weed while they are pregnant or breastfeeding.