In 20 breastfeeding mothers who used cannabis, THC accumulated in breast milk at a median concentration 7 times higher than in plasma, and mothers increased their cannabis use in the early postpartum period.
Breastfeeding mothers who use cannabis, obstetricians, pediatricians, and lactation consultants.
THC in breast milk was 7x higher than in blood plasma
What the researchers found
Median breast milk THC concentration was 27.5 ng/ml vs 3.7 ng/ml in plasma, a milk-to-plasma ratio of 7.0. CBD also concentrated in breast milk (M/P ratio 2.6). THC in breast milk increased by 30.2 ng/ml from visit 1 (2 weeks) to visit 2 (2 months). Mothers used cannabis frequently, with a median of 17-23 instances per week.
Why it matters
With increasing cannabis legalization and use during breastfeeding, quantifying how cannabinoids concentrate in breast milk is essential. The 7-fold concentration of THC relative to plasma means infants may receive meaningful cannabinoid exposure.
The numbers in context
20 subjects; median THC: plasma 3.7 ng/ml, milk 27.5 ng/ml; THC M/P ratio 7.0; CBD M/P ratio 2.6; cannabis use 17-23 instances/week; breast milk THC increased by 30.2 ng/ml from 2 weeks to 2 months
How the study worked
Prospective study at a university hospital in a state with legal cannabis. Twenty breastfeeding mothers who used cannabis in the last 48 hours provided breast milk and plasma samples at 2 weeks and 2 months postpartum, along with survey data on use patterns.
What this study cannot tell us
Small sample of 20 self-selected cannabis users. No measurement of infant cannabinoid levels. No assessment of infant health outcomes. Cannot determine clinical significance of exposure levels.
How to read the evidence
Prospective design with paired plasma and milk measurements, though small sample and no infant outcome data.
When this study was published
Published in 2021.
The bigger picture
The finding that cannabis use increased in the early postpartum period, combined with high milk-to-plasma ratios, means infant exposure may actually increase over the first two months of life, a period of critical neurodevelopment.
Questions still open
- What are the actual infant blood levels resulting from breastfeeding exposure? Does cannabinoid exposure via breast milk affect infant neurodevelopment? How long do cannabinoids persist in breast milk after the last use?
Common questions
Does THC get into breast milk?
Did mothers use more cannabis after giving birth?
Read the original research
Cannabis use and measurement of cannabinoids in plasma and breast milk of breastfeeding mothers.
Pediatric research, 90(4), 861-868
Citation
Moss, Michael J; Bushlin, Ittai; Kazmierczak, Steven; Koop, Dennis; Hendrickson, Robert G; Zuckerman, Katharine E; Grigsby, Tamara M. (2021). Cannabis use and measurement of cannabinoids in plasma and breast milk of breastfeeding mothers.. Pediatric research, 90(4), 861-868. https://doi.org/10.1038/s41390-020-01332-2
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