summary of key studies & research:

PUBMED - Surveying Lactation Professionals Regarding Marijuana Use and Breastfeeding

“Results: Of 120 conference attendees, 74 completed the survey. Forty-four percent reported their recommendations around breastfeeding and marijuana use depended on factors like the severity of maternal use. Another 41% reported recommending continued breastfeeding because the benefits outweigh the harms. The remaining 15% reported recommending that a woman should stop breastfeeding if she cannot stop using marijuana. Survey completers estimated that 15% (1,203/7,843) of their breastfeeding clients in the past year used marijuana.

Conclusions: Lactation professionals vary widely in their recommendations to breastfeeding clients who use marijuana. The estimate of prevalence also suggests this is a relatively common issue. More research is needed to assess the generalizability of these findings.“

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4692106/#:~:text=Survey%20completers%20estimated%20that%2015,is%20a%20relatively%20common%20issue.

PUBMED - Postpartum Marijuana Use, Perceptions of Safety, and Breastfeeding Initiation and Duration: An Analysis of PRAMS Data From Seven States, 2017

“Results: Overall, 5.5% (95% CI [4.6, 6.6]) of participants reported postpartum marijuana use; among these women, 47.2% (CI [37.6, 56.9]) were breastfeeding at the time of the survey. Overall, 25.7% of participants indicated that they had been advised, by their prenatal care provider, against marijuana use while breastfeeding. Breastfeeding initiation or duration did not differ by postpartum marijuana use. Among participants with postpartum use, those who perceived marijuana was safe for breastfeeding women to use were more likely to have breastfed (aPR = 1.22, CI [1.04, 1.43]) and have a breastfeeding duration > 12 weeks (aPR = 1.57, CI [1.08, 2.27]) compared to those who perceived it to be unsafe.

Conclusions: Understanding maternal safety beliefs and provider education about the latest evidence and guidance related to postpartum marijuana use may improve clinical care.”

https://pubmed.ncbi.nlm.nih.gov/33586506/

PUBMED - Medicinal Cannabis: History, Pharmacology, And Implications for the Acute Care Setting

“Regardless of personal views and perceptions, to deny or disregard the implications of use of this substance on patient health and the infrastructure of the health care system is irresponsible; clinicians must be aware of these implications and informed about how this therapy may influence practice in a variety of health care settings, including acute care.“

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5312634/

PUB MED - Marijuana Use by Breastfeeding Mothers and Cannabinoid Concentrations in Breast Milk

https://pubmed.ncbi.nlm.nih.gov/30150212/

Results: ∆9-THC was detectable in 34 (63%) of the 54 samples up to ∼6 days after last reported use; the median concentration of ∆9-THC was 9.47 ng/mL (range: 1.01-323.00). Five samples had detectable levels of 11-hydroxy-Δ-9-tetrahydrocannabinol (range: 1.33-12.80 ng/mL) or cannabidiol (range: 1.32-8.56 ng/mL). The sample with the highest concentration of cannabidiol (8.56 ng/mL) did not have measurable ∆9-THC. Cannabinol was not detected in any samples. The number of hours since last use was a significant predictor of log ∆9-THC concentrations (-0.03; 95% confidence interval [CI] -0.04 to -0.01; P = .005). Adjusted for time since last use, the number of daily uses and time from sample collection to analysis were also significant predictors of log ∆9-THC concentrations (0.51; 95% CI 0.03 to 0.99; P = .039; 0.08; 95% CI 0.00 to 0.15; P = .038, respectively).

The part I put in bold is an indication that some form of edible consumption was used as 11-hydroxy-∆-9-tetrahydrocannabinol is a metabolite formed in the GUT when active ∆9-THC is consumed orally and broken down that way rather than smoked!

NATIONAL LIBRARY OF MEDICINE - Drugs and Lactation Database - Cannabis

“The milk of cannabis users had lower levels of sIgA relative to non-users; however, when adjusted for BMI, there was no difference in sIgA levels between the groups.“

https://www.ncbi.nlm.nih.gov/sites/books/NBK501587/

This study also did not account for the use of tobacco products

SCIENCE DIRECT - Function of Cannabinoid Receptors in the Neuroendocrine Regulation of Hormone Secretion

“The acute effects of cannabinoids on the endocrine system are consistent with its actions on brain neurotransmitter systems involved in the regulation of neuropeptides that modulate anterior pituitary hormone secretion. Although cannabinoid receptors appear to play a major role in the ability of cannabinoids to influence hormone release, much remains to be learned concerning their function in the neuroendocrine regulation of hormone secretion.“

https://www.sciencedirect.com/science/article/abs/pii/S0969996198902248?via%3Dihub

SCIENCE DAILY - Breast milk of marijuana users does not hurt short-term health of early premature infants, long-term effects still unknown

https://www.sciencedaily.com/releases/2021/10/211008083531.htm

“Summary: Researchers compared early preterm infants who were fed breast milk from THC-positive mothers to those who were fed either formula or breast milk from THC-negative mothers and found no differences in short-term health impacts such as breathing difficulties, lung development, and feeding issues.”