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THC Lingers in Human Milk Hours After Cannabis Use

    Cannabis use during breastfeeding contains elevated levels of delta-9-tetrahydrocannibinol (THC).

    Written by: Brittany T. Truong, Ph.D. | Issue # 122 | 2024

    • Current guidelines from the CDC discourage cannabis use while breastfeeding due to limited scientific research on how long delta-9-tetrahydrocannibinol (THC), the primary psychoactive compound in cannabis, remains in human milk. 
    • In a new study, researchers found that THC concentrations in human milk were high but variable, depending on the frequency of cannabis use. 
    • It is unknown whether the THC in human milk influences infant development. 

    The legalization of cannabis in the United States has led to more widespread use, including among women of reproductive age [1, 2]. The CDC has taken a conservative approach and currently advises breastfeeding women to reduce or avoid cannabis use to limit the potential risk to infants; however, this guideline is rooted in little scientific evidence [3, 4].

    “For most of our lives, cannabis has been illegal,” says Michelle (Shelley) McGuire, director of the Margaret Ritchie School of Family and Consumer Sciences and a professor in the College of Agricultural and Life Sciences at the University of Idaho. There’s “shockingly little data” on how cannabis affects the composition of breast milk.

    “Parents really want that information,” says Courtney Meehan, a professor and interim dean for the College of Arts and Sciences at Washington State University. “The cannabis research world is new, and we’re playing catch-up.” 

    In a new prospective study, published in Breastfeeding Medicine, Meehan, McGuire, and colleagues show that in breastfeeding individuals who frequently use cannabis, delta-9-tetrahydrocannibinol (THC), the primary psychoactive compound, is detected in human milk [5]. 

    Breastfeeding mothers were asked to abstain from cannabis for 12 hours prior to the milk sample collection. After the abstention, participants collected a milk sample and were free to administer their own cannabis [5]. Due to ethical considerations, the research team did not provide the cannabis products to participants. 

    Participants were asked to collect full breast expression samples, meaning they expressed until there was no more milk [5]. This was particularly important as milk fat increases at the end of a feed, and THC is fat-soluble. Previous studies had not done this [3, 4].

    The researchers confirmed that THC can be measured in human milk following abstention and after single and repeated cannabis use. After single cannabis use, the time at which THC levels peaked was highly variable, ranging from 30 minutes to 1.25 hours [5]. 

    “This was surprising to us,” Meehan says. “It shows us that there are so many other variables that we can’t identify that might be contributing to that variation. In the future, understanding those variables is going to be really important.” 

    The researchers also found that THC concentrations in human milk increased when cannabis was used more frequently [5]. 

    The data suggest that cannabis is distinct from alcohol, which has been shown to peak in human milk 30-60 minutes after consuming an alcoholic beverage [6].

    “There is an assumption among some cannabis users that alcohol and cannabis will behave the same and that individuals who use cannabis can predict the timing of its peak and decline in human milk,” says Meehan.

    The researchers estimated that an infant would consume a median of 0.0052 mg/kg of body weight of THC in a single feed [5]. It is not known if there are any impacts on the nursing baby. The lowest level of THC in milk that has been observed to have an adverse effect is 0.036 mg/kg of body weight [7]. 

    “We know nothing about the potential effects on babies. Zero,” says McGuire. “A lot of things show up in milk and have no effect on the baby. The proof is going to be in the pudding. Until then, we can say nothing.” 

    But the research looking at short- and long-term effects on developing infants has been slow. According to Meehan and McGuire, one of the reasons is that breastfeeding women have historically been excluded, forgotten, and under-studied.

    McGuire says, “It’s a systemic problem, especially considering how important breast milk is for the baby’s development.” 

    Indeed, human milk is considered the “gold standard” for infant nutrition due to its positive effects on early neurodevelopment and the immune system. Therefore, future studies looking at the effects of cannabis use on infant development are critical. 

    Moreover, cannabis use among postpartum women has significantly increased in states that have legalized it [2]. In a related study published earlier this year, Meehan, McGuire, and colleagues show that many nursing women are using cannabis products, not for recreation, but to treat or manage health conditions, usually related to mental health [8]. 

    “Women are not passively making the decision (to use cannabis),” says Meehan. “They are actively seeking out information and actively weighing the costs and benefits of doing this. These women are working hard to make the best decisions based on the available information that they can find.” 

    Meehan adds that when conducting these studies, “It’s critical for us that we avoid stigmatizing women.

    “We’re scientists here — completely agnostic with no value judgment,” says McGuire. “We just feel like women need evidence-based information.”

    References

    1. Alshaarawy O, Anthony JC. Cannabis use among women of reproductive age in the United States: 2002-2017. Addict Behav. 2019 Dec;99:106082.
    2. Skelton KR, Hecht AA, Benjamin-Neelon SE. Association of recreational cannabis legalization with maternal cannabis use in the preconception, prenatal, and postpartum periods. JAMA Netw Open. 2021 Feb 1;4(2):e210138.
    3. Bertrand KA, Hanan NJ, Honerkamp-Smith G, Best BM, Chambers CD. Marijuana use by breastfeeding mothers and cannabinoid concentrations in breast milk. Pediatrics. 2018 Sep;142(3).
    4. Wymore EM, Palmer C, Wang GS, Metz TD, Bourne DWA, Sempio C, et al. Persistence of Δ-9-tetrahydrocannabinol in human breast milk. JAMA Pediatr. 2021 Jun 1;175(6):632-4.
    5. Holdsworth EA, Berim A, Gang DR, Williams JE, Smith CB, Caffé B, et al. Human milk cannabinoid concentrations and associations with maternal factors: The lactation and cannabis (lac) study. Breastfeed Med. 2024 Jul;19(7):515-24.
    6. Drugs and Lactation Database (LactMed®) [Internet]. National Institute of Child Health and Human Development. 2006– [cited August 2, 2024]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK501469/.
    7. EFSA CONTAM Panel (EFSA Panel on Contaminants in the Food Chain). Scientific opinion on the risks for human health related to the presence of tetrahydrocannabinol (thc) in milk and other food of animal origin. EFSA Journal. 2015;13(6):4141.
    8. Smith CB, Schmidt J, Holdsworth EA, Caffe B, Brooks O, Williams JE, et al. Cannabis use, decision making, and perceptions of risk among breastfeeding individuals: The lactation and cannabis (lac) study. J Cannabis Res. 2024 Feb 16;6(1):6.