JAMA Pediatrics published a study that measured tetrahydrocannabinol (THC) levels in breast milk and plasma in seven female cannabis users who had recently given birth in Colorado. Researchers found that the milk:plasma partition coefficient for THC was approximately 6:1, and that the compound has an estimated mean half-life in breast milk of 17 days.
The team could not determine how long THC remains detectable in the breast milk of recent mothers, but it is clear that it is at least six weeks in regular cannabis users. All seven women involved still had detectible concentrations of THC in their breast milk at the end of the six-week study. The researchers—led by Erica Wymore, MD, MPH, neonatologist at Children’s Hospital Colorado and assistant professor of pediatrics at the University of Colorado School of Medicine on the Anschutz Medical Campus—noted that concentration varied from woman to woman and were impacted by level of use, body mass index, and metabolism.
Additionally, the team found that THC levels actually spike in new mothers two weeks following birth, and then begin decreasing. “This phenomenon may be attributable to changing fat composition in breast milk in the early postpartum period, individual metabolism, and differences in marijuana use patterns,” the researchers wrote.
According to a release from the Children’s Hospital, all women involved in the study met the following conditions:
Claimed to have had a history of marijuana use during pregnancy
Had detectible levels of THC in their urine when admitted for delivery
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
Were over the age of 18
A total of 394 women were screened. Of those 394, 25 enrolled in the study. Of the 25 who enrolled, only 7 abstained from marijuana use for the duration of the six-week study.
JAMA Pediatrics has more.