After mothers used cannabis, breast milk showed lower lipid levels and altered fatty acid profiles for several hours, with THC levels correlating positively with fat and negatively with lactose.
Breastfeeding researchers, lactation consultants, maternal health providers
10 of 39 fatty acids measured were lower in milk after cannabis use
What the researchers found
Cannabis use was associated with temporarily lower lipid and fatty acid concentrations and blunted lactose increase in breast milk; THC levels correlated positively with lipids and negatively with lactose.
Why it matters
Cannabis use among breastfeeding women is increasing, but almost nothing is known about how it affects milk nutritional composition beyond cannabinoid transfer.
The numbers in context
20 cannabis users, 19 controls; lipid and 10 of 39 identified fatty acids were lower after use; no baseline differences between groups; no protein differences at any timepoint.
How the study worked
Within-subjects design with 20 breastfeeding cannabis users matched with 19 non-using controls by BMI and time postpartum; cases abstained 12+ hours, collected baseline milk, used cannabis, then collected samples at multiple timepoints up to 8-12 hours.
What this study cannot tell us
Small sample (n=39 total); single cannabis use session; did not measure infant outcomes; could not control for cannabis product variation; THC as the measured cannabinoid may not capture full effects.
How to read the evidence
Well-designed matched study with repeated sampling, but small sample size and single-session design limit generalizability.
When this study was published
Published 2025
The bigger picture
This adds a nutritional dimension to the discussion about cannabis and breastfeeding, beyond the known issue of THC transfer to infants.
Questions still open
- Do repeated cannabis use sessions produce cumulative effects on milk composition? Could these transient changes affect infant nutrition or growth? What mechanisms drive the lipid decrease?
Common questions
Did cannabis change the nutritional content of breast milk?
Was protein affected?
Read the original research
Short-Term Effects of Maternal Cannabis Use on Human Milk Macronutrient Composition: The Lactation and Cannabis (LAC) Study.
Breastfeeding medicine : the official journal of the Academy of Breastfeeding Medicine
Citation
Castro-Navarro, Irma; Williams, Janet E; Dussurget, Léa; Richardson, Haley; Berim, Anna; Gang, David R; Holdsworth, Elizabeth A; Caffé, Beatrice; Smith, Caroline; Barbosa-Leiker, Celestina; Brooks, Olivia; McGuire, Mark A; Meehan, Courtney L; McGuire, Michelle K. (2025). Short-Term Effects of Maternal Cannabis Use on Human Milk Macronutrient Composition: The Lactation and Cannabis (LAC) Study.. Breastfeeding medicine : the official journal of the Academy of Breastfeeding Medicine. https://doi.org/10.1177/15568253251407688
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