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Research Shows That THC Stays in Breast Milk for Six Weeks

In a new study published in JAMA Pediatrics, researchers at Children’s Hospital Colorado have found that tetrahydrocannabinol (THC), the psychoactive component of marijuana, stays in breast milk for up to six weeks, further supporting the recommendations of the American Academy of Pediatrics, the American College of Obstetricians and Gynecologists and the Academy of Breastfeeding Medicine to abstain from marijuana use during pregnancy and while breastfeeding. This is the first study examining THC in breastmilk and plasma among women with known marijuana use in pregnancy since a 1982 study in the New England Journal of Medicine.

How the Study was Conducted

The researchers studied women with prenatal marijuana use who delivered their infants at Children’s Colorado and University of Colorado Hospital between November 1, 2016, and June 30, 2019. Specifically, researchers recruited women who:

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

Of the 394 women who were screened, 25 enrolled. Seven of these women were ultimately able to abstain from marijuana use for the duration of the study. The study found that, while the concentrations of THC varied from woman to woman, THC was excreted in the breast milk of these seven women for up to six weeks. In fact, all the women still had detectable levels of THC in their breastmilk at the end of the study.

What the Study Revealed

The researchers who conducted this study say that it not only provided insight into the length of time it takes a woman to metabolize the THC in her body after birth, but it also helped understand why mothers use marijuana in the first place. To limit the unknown THC effects on fetal brain development and promote safe breastfeeding, experts emphasize marijuana abstention both early in pregnancy and postpartum. To help encourage successful abstention, the researchers hope that the insights gained from this study will improve the systems of support offered to new moms.

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