Cannabis and Breastfeeding

Abstract

The complex issues surrounding cannabis^* use during breastfeeding have been well detailed by Mourh and Rowe in this issue of Breastfeeding Medicine.¹ One topic that requires some amplification is that of assay methodology. The high fat solubility of cannabinoids makes them difficult to analyze in breast milk. Only in the past 2 years have sensitive and reliable methods been reported.^2,3 The oft-quoted breast milk tetrahydrocannabinol (THC) levels reported in a 1982 letter to the editor used a poorly characterized assay methodology that might not be accurate.⁴ Also, the portion of milk (i.e., foremilk versus hindmilk) that was analyzed was not stated and the unusually high milk/plasma ratio of 8+ was not calculated correctly by modern standards. More recent articles have reported somewhat lower levels of THC in the breast milk of recreational users,^2,5 despite the fact that cannabis products have become more potent over the years. Nevertheless, the World Health Organization Working Group used data from the 1982 report and another study to estimate that the infant receives a rather low 0.8% of the maternal weight-adjusted dosage or relative infant dose.⁶ Another somewhat reassuring factor is that the oral bioavailability of THC is only 2% to 14%, at least in adults.⁷ The twin problems, of course, are that we usually do not know what dose the users ingested or when it was ingested, and we have no idea what the levels found in milk mean for the infant.

Prospects for More Data

The unbelievably small amount of information on the excretion of cannabis components into breast milk is partly the result of cannabis products being a Schedule I controlled substance in the United States, meaning that it has “no currently accepted medical use in treatment in the United States, a lack of accepted safety for use under medical supervision, and a high potential for abuse.” The United States Drug Enforcement Administration (DEA) has had a tight grip on cannabis research, making the drug difficult to study. Although this might be loosening, interventional studies that DEA does approve must use cannabis from the government's farm at the University of Mississippi. This product has been found recently to have only a relatively low 8% THC, as well as being contaminated with mold and lead.⁸ As a result, although cannabis is being widely used, we have very little relevant information in humans, especially during lactation. Since most, if not all, institutional review boards would be unlikely to approve a study that provided cannabis to nursing mothers for research purposes, other research strategies must be found. This has been made easier by the change in legal status of the drug in many states, giving some measure of protection to cannabis users who volunteer for research.

One method of studying cannabinoids in breast milk is the analysis of donor milk from mothers who have used the drug. Mommy's Milk, a human milk biorepository at the University of California San Diego, has collected breast milk from women recruited through social media and several clinical sites around San Diego. Participants who reported using cannabis within the 7 days before sample collection completed an interview on demographics, time and type of cannabis ingestion, health history, and lifestyle habits (i.e., medications, recreational drugs, tobacco, and alcohol). The first 54 milk samples have been analyzed using a sensitive new method for THC, hydroxy-THC, cannabinol, and cannabidiol. Data are being analyzed for an upcoming publication. Although these samples will greatly add to our knowledge about excretion of cannabinoids into breast milk, they will still fall short of providing a clear answer about any long-term effects on breastfed infants. For example, of the first 14 women who provided samples, 57% had a mental illness diagnosis, such as anxiety or depression, and 86% had also consumed alcohol within the prior 7 days.^9,10 If these women are representative of all mothers who use cannabis while breastfeeding, it will take a very large study indeed to untangle all of the confounding factors that could be affecting their infants!

The issue of non-THC cannabinoids in breast milk raises some interesting issues. One purported use of cannabidiol is for the treatment of refractory seizures. It is not psychoactive in the sense of THC, so would appear not to fit into the Schedule I classification. The DEA is apparently open to reclassifying it once adequate studies show efficacy. Currently, many families are traveling, or even relocating, to Colorado so they can obtain cannabidiol for an affected child. Dr. Amy Brooks-Kayal, from the University of Colorado–Denver, gave a talk earlier this year at a meeting of teratology professionals entitled, “Cannabinoids for Treatment of Pediatric Epilepsy: The Hype and the Evidence.”¹¹ Her experience with the analysis of available products is that “cannabidiol” products that are available on the cannabis market in Colorado are all to some extent mixtures that also contain THC. This situation makes it difficult to come to any conclusions regarding the efficacy and safety of cannabidiol in pediatric epilepsy. It also implies that nursing mothers who think they are taking cannabidiol are also transferring THC and probably other cannabinoids into breast milk.

Long-term human studies on infant outcomes after maternal cannabis use during breastfeeding are limited to two old small studies with somewhat inadequate methodology. Many of the mothers also used cannabis during pregnancy, which is probably more risky than use during breastfeeding and complicates the findings. Various animal studies of questionable relevance to humans have found inconsistent outcomes for many endpoints.¹ It is no wonder that a recent survey in Colorado, where use of both medical and recreational cannabis is legal, found that although health professionals are generally knowledgeable about the state cannabis laws, few felt completely knowledgeable about cannabis nor do they feel entirely confident talking to patients about this issue.¹² Sharp differences of opinion on cannabis have also been voiced regarding the Academy of Breastfeeding Medicine's Clinical Protocol on substance abuse.^13,14

Advising Mothers

So, given this lack of reliable information, what should we do? A few things are fairly clear. Everyone would agree that nursing mothers should not use cannabis during breastfeeding. However, what do we tell mothers who vow to continue cannabis use while breastfeeding. In this case, if we believe that the benefits of breastfeeding probably outweigh the risks of cannabinoids in breast milk, we can recommend that the mother reduce cannabis consumption and avoid smoking in the same room with the infant or otherwise avoid exposing the infant to second-hand smoke. Avoiding infant contact with clothing and other items that might have cannabis residue on the surface might also be helpful. It seems fair to point out to mothers that cannabis compounds will likely appear in their breast milk for days to weeks after use and in the feces and perhaps urine of their infant from the drug in breast milk.⁴ Positive test results might have negative legal implications in some states. Unlike with tobacco smoking and some other recreational drug use, it is not possible at our current state of knowledge to advise mothers about the timing of breastfeeding after cannabis use because of its persistence in their body and lack of good data. It seems fair to tell a mother that her cannabis use is unlikely to benefit her infant, but based on current evidence, we honestly and unfortunately do not know whether it will do harm.

Footnotes

Disclosure Statement

No competing financial interests exist.

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