Mother breastfeeding baby

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AURORA, Colo. — Just as smoking and drinking during pregnancy can have a negative impact on a child’s development, a new study finds marijuana use even after the delivery can be detrimental to a newborn. Researchers at Children’s Hospital Colorado say tetrahydrocannabinol (THC), the psychoactive component of marijuana, remains in a woman’s breast milk for at least six weeks. The revelation is creating a widespread push by health organizations to get mothers to abstain from using pot, even as more states legalize its use.

“With the increasing utilization of marijuana in society as a whole, we are seeing more mothers who use marijuana during pregnancy,” says primary investigator and neonatologist Erica Wymore, in a media release.

“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.”

The study is the first in nearly 40 years to examine THC levels in a mother’s milk among women who admit to using cannabis. The American Academy of Pediatrics, the American College of Obstetricians and Gynecologists, and the Academy of Breastfeeding Medicine all recommend avoiding the drug entirely while pregnant or breastfeeding.

Mothers could pass on THC for months

In the new report, researchers studied a group of women delivering their babies at Children’s Colorado and UCHealth’s University of Colorado Hospital between November 2016 and June 2019. The women also had to meet specific criteria including having a history of marijuana use and testing positive for THC when entering the hospital.

The women had to be over 18 and have an intention to breastfeed. They also had to agree to abstain from marijuana for six weeks after delivery and continually give milk, blood, and urine samples during the experiment.

Of the nearly 400 women screened by researchers, just 25 enrolled in the study. Out of these expecting mothers, only seven successfully abstained from marijuana for the full six weeks. For the 18 who couldn’t go without cannabis, the reasons they gave included stress, sleep issues, and a need to manage pain.

Despite only seven making it to the end, the results reveal all of these women had detectable concentrations of THC in their milk six weeks after delivery. Although the amounts varied depending on level of use, body mass index, and their metabolism, researchers say THC was still present even after the study ended.

“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,” says Maya Bunik, MD, MPH, medical director of the Child Health Clinic and the Breastfeeding Management Clinic at Children’s Colorado.

“To limit the unknown THC effects on fetal brain development and promote safe breastfeeding, it is critical to emphasize marijuana abstention both early in pregnancy and postpartum. To help encourage successful abstention, we need to look at – and improve – the system of supports we offer new moms.”

40 years of evidence on marijuana and pregnancy

Researchers say studies from the 1980s also discovered how the children of marijuana-using mothers could experience long-term health problems. These issues include cognitive and executive function impairments and learning deficits — especially with attention and visual problem-solving skills.

“This study was not about the impact marijuana has on babies, but we are concerned,” Wymore concludes. “Especially when we consider that today’s marijuana is five to six times higher in potency than what was available prior to recent marijuana legalization in many states.”

The study appears in the journal JAMA Pediatrics.

About Chris Melore

Chris Melore has been a writer, researcher, editor, and producer in the New York-area since 2006. He won a local Emmy award for his work in sports television in 2011.

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