There is no medicine like mother’s milk. It is the primary source of nutrition that newborns receive. Breast milk contains everything a baby needs to continue growing. It provides all the essentials to maintain survival including protein, fat, carbohydrates, vitamins, and minerals. A baby’s consumption of breast milk also contributes to the development of a healthy gut microbiome and immune system. This in turn protects them from infection and inflammation.  Many of these mechanisms are modulated by the endocannabinoid system.
The endocannabinoid system has an essential role in how newborns eat and receive nutrients. A baby’s suckling instinct is essential for survival. CB1 receptor signaling triggers this intuitive mechanism.  Endocannabinoids are also present in mother’s milk. Breast milk is enriched with arachidonic acid, a building block of the body’s own endocannabinoids anandamide and 2-AG. Arachidonic acid boosts endocannabinoid levels which is essential for newborn brain development both before and after birth. Endocannabinoids bind to CB1 and CB2 receptors which also mediate many of the effects of cannabis. 
Cannabinoid Accumulation in Breast Milk
Cannabis use is becoming increasingly popular, and many women are curious about the ways in which the plant impacts pregnancy and breastfeeding. As is the case with cannabis research, we have much more to learn. We do know that if a mother uses cannabis while breastfeeding, so does her baby. When a mother smokes or vaporizes cannabis with THC in it, she almost completely converts it into inactive metabolites in about three hours. Orally ingested forms of cannabis may linger for five to 10 hours. 
A 2018 study by Baker and colleagues found that Delta-9-THC was transferred to nursing infants at a concentration of around 2.5% of the maternal dose. Levels of THC and its metabolites have been detected in the organs of babies. Also, lower levels of THC metabolites have been found in infant fecal samples. 
Three studies examined the concentrations of cannabinoids in breast milk and plasma. All of them came to similar results:
- It takes about six weeks for cannabinoids to be completely eliminated from breast milk.
- There is a 17 day half-life of THC in milk (a half life is the amount of time a substance takes to decrease its level in the body in half).
- THC is lipophilic and more of it accumulates in breast milk.
- The presence of active metabolite 11-OH-THC is minimal because it is more water soluble than THC.
- With oral cannabis ingestion, cannabinoid levels are lower in both the mothers’ milk and plasma.
- However, both oral ingestion and smoking create cannabinoid concentrations in breast milk. [4,5,6]
These findings indicate that there is less exposure with oral intake of cannabis as opposed to inhalation. Oral intake has a first pass effect, metabolizing to 11-OH-THC, which is more water soluble than Delta-9-THC. In addition, the 17 day half-life makes the act of “pump and dump” ineffective. Pump and dump is when the mother uses a breast pump to collect milk and throws it out instead of allowing the baby to drink it. This is done in an effort to decrease the amount of THC the infant is exposed to. This practice is founded upon the concept that the second round of milk would not contain cannabinoids or other substances. It also must be noted that we do not know the clinical impact, if any, that low doses of cannabinoids would have on a nursing baby.
What about the presence of CBD in breast milk? In a 2021 study by Moss and colleagues, 20 mothers using cannabis were surveyed by a university hospital in Oregon. There were 22 participants and three of them used CBD. Milk has a high lipid content so lipophilic substances such as THC will accumulate in it. CBD has been found to accumulate in breast milk, but to a lesser extent than THC. [6,7]
The Impact of Cannabis on Breastfeeding Newborns
There is an overall lack of human data on how cannabis use while breastfeeding affects the newborn. For example, the impact of cannabis on the baby is difficult to determine if the mother used cannabis during pregnancy. There are also other considerations such as the use of alcohol, tobacco, etc. These factors and more demonstrate the research challenges of studying the effects of cannabis on breastfeeding babies.
Some studies show low psychomotor development in nursing infants with mothers using cannabis. Others show no effect on mental or motor development. [8,9] However, these are old studies with data from decades prior. Also, little is known about how other cannabinoids beyond THC and CBD transfer into human milk.
There is currently no collective consensus on the use of cannabis while breastfeeding among organizational groups that focus on pediatric health. The American College of Obstetricians and Gynecology, the American Academy of Pediatrics, and the Academy of Breastfeeding Medicine do not state that the use of cannabis is a contraindication to breastfeeding. Rather, breastfeeding is encouraged while the use of cannabis is discouraged. 
In summary, research on cannabis while nursing has been largely inconclusive. This is because studies have been confined to very small or highly selected subgroups. Research often relies exclusively on self-reports or medical records to determine if other substances were used. Some of them did not control for important confounding factors, whether they were alcohol or other drug use, nutrition, etc.
Considerations Before Using Cannabis & Legal Cautions
The wellbeing of both the patient and the baby must be regarded first and foremost. A mother and her physician must weigh the pros and cons of cannabis use while breastfeeding. The benefits need to far outweigh the risks. Patients should be informed about current research studies and be aware that further research is needed. 
In general, it is not recommended to use cannabis “recreationally” while pregnant or breastfeeding. If cannabis is the most viable medicine for a nursing mother, the lowest effective dose should be used to relieve symptoms. An oral route of administration, as opposed to inhalation, is preferred in order to decrease the baby’s exposure. Since edibles may be perceived as less harmful than smoked cannabis, breastfeeding mothers should be aware of the potential of THC to accumulate in breast milk after using them. 
Additional Factors to Take into Account
Examining the data thus far, mandatory reporting or legal ramifications for cannabis use during pregnancy or breastfeeding are not medically warranted. Appropriate counseling of breastfeeding women is both essential and effective for behavior adjustment. Clinicians and healthcare providers should keep the lines of communication open. No woman wants to hurt her baby. Physicians should bring up the subject of cannabis use in a nonjudgmental way. If needed, they can help patients find a different choice of medicine. Clinicians can also use a dose, chemovar, or route of administration that decreases the potential amount of exposure to the infant.
There are instances in which cannabis use can be necessary or used as harm reduction. For example, a woman may use cannabis because it is the only medication that controls (and potentially eliminates) her seizures. In this instance, cannabis while nursing may be an appropriate choice of medication. Women with chronic pain disorders, PTSD, and other ailments sometimes use cannabinoid therapies as their only means to function. Again, both the healthcare professional and patient must weigh the options to discern if cannabis is indeed the most viable treatment option.
In conclusion, we now have clear scientific evidence that cannabinoids such as CBD and THC accumulate in breast milk. Attempts to decrease the amount of cannabis the baby is exposed to after the fact are ineffective. Beyond that, more research is needed to determine the effects on the infant while breastfeeding. In the meantime, well-informed clinicians must support and educate their patients via a lens of compassion.
- Australian Breastfeeding Association. (2017). Breastmilk composition. Accessed on 2/9/2022
- Fride, E. (2008). Multiple roles for the endocannabinoid system during the earliest stages of life: pre and postnatal development. Journal of Neuroendocrinology, 20, 75-81.
- Lee, Martin A. (2017). DIET & THE ENDOCANNABINOID SYSTEM. Project CBD. Accessed on 2/9/2022
- Wymore, E. M., Palmer, C., Wang, G. S., Metz, T. D., Bourne, D. W., Sempio, C., & Bunik, M. (2021). Persistence of Δ-9-Tetrahydrocannabinol in Human Breast Milk. JAMA pediatrics, 175(6), 632-634.
- Baker, T., Datta, P., Rewers-Felkins, K., Thompson, H., Kallem, R. R., & Hale, T. W. (2018). Transfer of inhaled cannabis into human breast milk. Obstetrics & Gynecology, 131(5), 783-788.
- Moss, M. J., Bushlin, I., Kazmierczak, S., Koop, D., Hendrickson, R. G., Zuckerman, K. E., & Grigsby, T. M. (2021). Cannabis use and measurement of cannabinoids in plasma and breast milk of breastfeeding mothers. Pediatric Research, 90(4), 861-868.
- Sempio, C., Wymore, E., Palmer, C., Bunik, M., Henthorn, T. K., Christians, U., & Klawitter, J. (2021). Detection of Cannabinoids by LC–MS-MS and ELISA in Breast Milk. Journal of Analytical Toxicology, 45(7), 686-692.
- Astley, S. J., Clarren, S. K., Little, R. E., Sampson, P. D., & Daling, J. R. (1992). Analysis of facial shape in children gestationally exposed to marijuana, alcohol, and/or cocaine. Pediatrics, 89(1), 67-77.
- Kreye, M. (1985). Marijuana: prenatal and postnatal exposure in the human. Current research on the consequences of maternal drug abuse, 85(1400), 48.
- Wilson-King, Genester. (2021). Cannabis Use in Pregnancy & Breastfeeding. SCC Clinical Training Curriculum.
- Hill, M., & Reed, K. (2013). Pregnancy, breast-feeding, and marijuana: a review article. Obstetrical & gynecological survey, 68(10), 710-718.
- National Academies of Sciences, Engineering, and Medicine. (2017). The health effects of cannabis and cannabinoids: the current state of evidence and recommendations for research.