THC found in breast milk up to 6 weeks after abstention
Women continued to excrete THC in breast milk for up to 6 weeks — and possibly longer — after abstaining from using marijuana, according to a study published in JAMA Pediatrics.
Erica M. Wymore, MD, MPH, a specialist in neonatal and perinatal medicine at Children’s Hospital Colorado, and colleagues performed a prospective, observational pharmacokinetic study of women with prenatal marijuana use who delivered infants between Nov. 1, 2016, and June 30, 2019.
A total of 394 women were screened for inclusion. Of these women, 105 were eligible and 25 were enrolled.
Criteria for study inclusion was an intention to breastfeed and marijuana abstention for 6 weeks. Study participants reported on substance use patterns, as well as provided maternal plasma and breast milk samples two to five times per week. Each sample was frozen for periodic batched analysis.
Of the 25 women enrolled, only 12 who self-reported abstinence from marijuana were actually abstinent based on plasma analysis results.
An analysis was performed on 402 matched plasma-milk samples. THC was the predominant compound found in the samples, with negligible concentrations of hydrophilic THC metabolites.
Every participant had detectable THC in their breast milk samples throughout the study. Within the first week postpartum for women who abstained, median THC concentrations were 3.2 ng/mL (interquartile range [IQR] = 1.2-6.8). This increased to 5.5 ng/mL (IQR = 4.4-16) at 2 weeks and declined to 1.9 ng/mL (IQR = 1.1-4.3) after 6 weeks.
The authors reported that the milk-to-plasma partition coefficient for THC was 6:1 (IQR = 3.8:1-8.1:1).
“To limit THC effects on fetal brain development and promote safe breastfeeding, it is critical to emphasize marijuana abstention both early in pregnancy and postpartum,” the authors wrote.
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It's a small study, but it provides some very intriguing information that cannot be ignored, and that brings up a series of questions regarding the importance of having a better understanding of the bioavailability in the exposure of babies that may be drinking milk from their mothers who have been smoking marijuana.
It does point out that the clearance rate of THC, which is the active ingredient of marijuana, in the milk is actually quite long. The half-life or clearance, according to this paper, is 17 days, and levels are not negligible. The paper has some very interesting findings — the concentration of THC in milk to that in blood is 6:1. It concentrates in the milk, which in a way is not surprising, because THC is extremely liquid soluble. So, it favors lipid areas, and the greater the content of the lipids in the milk, the higher the content of THC.
I was thinking about it, and the things that I would have liked to see, would be an understanding of what the content of THC is going to be in the baby who is drinking that milk, because that's ultimately the variable that will determine whether there is a concern. I mean, there is a concern because we don't really know how harmful it is, but to the extent that we could determine the levels that are reaching that baby, that would give us an even better perspective. It's a fascinating study.
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