Psychoactive ingredient in marijuana can stay in breast milk for six WEEKS after giving birth

The psychoactive ingredient in marijuana can remain in breast milk for up to six weeks after mothers quit using the drug, a new study suggests.

Researchers found levels of tetrahydrocannabinol (THC) were as high as 5.5 nanograms per milliliter (ng/mL) two weeks after women gave birth.

This is higher than the blood THC level of five ng/mL or higher needed to charge drivers with a DUI (driving under the influence), in some states. 

By six weeks post-delivery, the THC levels in breast milk had dropped to about two ng/mL, low but still detectable.

The team, from the University of Colorado School of Medicine, says its findings support recommendations from several groups, including the American Academy of Pediatrics, the Academy of Breastfeeding Medicine and the American College of Obstetricians and Gynecologists to abstain from pot use during pregnancy and while breastfeeding.  

A new study found that, within two weeks of giving birth, new mothers had levels of tetrahydrocannabinol (THC) of 5.5 nanograms per milliliter (ng/mL) in their breast milk (above)

‘With the increasing utilization of marijuana in society as a whole, we are seeing more mothers who use marijuana during pregnancy,’ said lead author Dr Erica Wymore, an assistant professor of pediatrics at the School of Medicine. 

‘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 the study, published in JAMA Pediatrics, the team looked at women who used marijuana prior to their infants being born in Colorado between November 1, 2016, and June 30, 2019.

All of the women were over the age of 18, had a history of marijuana use when admitted for delivery, had an intention to breastfeed and were willing to abstain from marijuana use for six weeks after delivery.

Of the 394 women who were screened, 25 were enrolled and seven were able to restrain from using cannabis for the duration of the study.  

All of the women, regardless of whether or not they completed the study, had concentrations of THC in their breast milk throughout the study, although how much varied from woman to woman. 

By six weeks post-delivery, the THC levels in breast milk had dropped to about two ng/mL, low but still detectable (file image)

By six weeks post-delivery, the THC levels in breast milk had dropped to about two ng/mL, low but still detectable (file image)

Within two weeks of giving birth, the women had THC concentrations of 5.5 ng/mL in their breast milk.

By week six post-partum, this had fallen to 1.9 ng/mL.

‘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,’ said senior investigator Dr Maya Bunik,  professor of pediatrics at the School of Medicine. 

‘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.’ 

Recent research has shown that self-reported marijuana use among pregnant women has exponentially risen.

Between 2002 and 2017, use increased two-fold from 3.4 percent to seven percent, according to the National Institute on Drug Abuse.

The Centers for Disease Control and Prevention (CDC) states that cannabis use during pregnancy can lead to low birth weight, attention issues and development disabilities.

A study from April 2019 found that pregnant women who use marijuana heavily to treat morning sickness affect part of the baby’s brain associated with memory.

Another study from August 2020 found that expecting mothers who used pot were 1.5 times more likely to have a child diagnosed with autism.  

‘This study was not about the impact marijuana has on babies, but we are concerned,’ said Wymore.

‘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.’