THC in marijuana can linger in breast milk for up to 6 weeks

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  • New research revealed that THC in marijuana can remain in breast milk six weeks after use
  • THC exposure has been negatively linked with the development of babies' brains
  • To encourage abstention from marijuana-use during pregnancy, better support should be offered to new moms

Health agencies, such as the US Food and Drug Administration (FDA), have previously warned that using marijuana while breastfeeding can harm one’s baby. To put it into context, it is  tetrahydrocannabinol (THC), the psychoactive ingredient in marijuana, that may negatively affect a newborn’s brain.

The American Academy of Paediatrics and the US Centers for Disease Control and Prevention (CDC) have also advised women to abstain from marijuana use during pregnancy and while they are breastfeeding, as THC is stored in fat and slowly released over time.

A new study, published in JAMA Pediatrics, further supports these recommendations. According to the findings, THC can remain in breast milk for up to six weeks after marijuana use.

The researchers, from the Children's Hospital Colorado, said that theirs is the first study, since a 1982 study, to test for THC in breast milk and plasma among women with known marijuana use in pregnancy.

Lead author of the study, Professor Erica Wymore, neonatologist at Children's Colorado explained that with the increasing utilisation of marijuana in society as a whole, doctors are seeing more mothers who use marijuana during pregnancy.

"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,” she went on to say.

With their latest study, they were able to better understand this question by looking at the amount and duration of THC excretion in breast milk among women with known marijuana use before giving birth.

Who were enrolled

The group of women that were studied delivered their babies at Children's Colorado and UC Health's University of Colorado Hospital between November 2016 and June 2019. The women had to meet the following criteria to be enrolled in the study:

  • Were over the age of 18
  • Had a history of marijuana use during pregnancy or a positive urine test for THC when admitted for delivery.
  • Had the intention to breastfeed
  • Were willing to abstain from marijuana use six weeks after delivery
  • Were willing to provide milk, blood and urine samples during this period

A total of 394 women were screened, but only 25 enrolled, with seven of them being able to abstain from marijuana use for the duration of the study.

While the concentrations of THC varied from woman to woman – which the researchers said was likely due to each woman’s level of use, BMI and metabolism – the mind-altering substance was excreted in the breast milk of all seven women for up to six weeks after they quit using it. 

Improving support for new moms

"This study provided invaluable insight into the length of time it takes a woman to metabolise the THC in her body after birth, but it also helped us understand why mothers use marijuana in the first place," said study co-author, Professor Maya Bunik, medical director of the Breastfeeding Management Clinic at Children's Colorado.

Bunik explained that to limit the unknown THC effects on foetal brain development and promote safe breastfeeding, it is critical that women abstain from marijuana use both early in pregnancy and postpartum.

“To help encourage successful abstention, we need to look at – and improve – the system of support we offer new moms," she added.

THC’s effect on baby’s brain: what studies have shown

According to the authors, studies from the 1980s showed that children born to mothers who used marijuana during pregnancy experienced long-term issues with cognitive and executive functioning (mental processing and skills), such as impulsivity, deficits in learning, and sustained problems with attention and visual problem-solving skills.

General guidance by the US CDC states that although more research is needed to better understand how marijuana use may affect your baby during pregnancy, pregnant women are advised to abstain from use.

It points to a 2013 and 2016 study that shows that marijuana use during pregnancy can cause health problems in newborns, including low birth weight. Another study showed that marijuana smoke contains many of the same chemicals as tobacco smoke, and could increase the chances of developmental problems in a baby.

According to Whymore, their study was not about the impact marijuana has on babies, but the findings do concern them: "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," she said.

READ | Marijuana is bad news for baby during pregnancy

READ | More pregnant women using dagga than ever before

READ | Self-medicating chronic migraines with cannabis may not be the best idea - more headaches can follow

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