It is difficult to study the effects of cannabis use during lactation due to the reliance on self-reported data or urine toxicology at time of delivery, which may not accurately capture the full details of exposure such as dose and frequency throughout the pregnancy. However, in light of the potential risk of negative obstetric outcomes, the American College of Obstetricians and Gynecologists (ACOG) and the American Academy of Pediatrics (AAP) discourages cannabis use during pregnancy and lactation.1,2
Cannabis exerts its effects via compounds called cannabinoids, with Delta-9 tetrahydrocannabinol (THC) being the most psychoactive.1,2 Cannabinoids primarily act on the central nervous system via cannabinoid receptor 1 (CB1) and immune system tissues via cannabinoid receptor 2 (CB2). The onset and duration of action of THC depends on the route of exposure.
Use During Lactation
There are insufficient data to evaluate the effects of cannabis use on infants during lactation and breastfeeding. Studies have shown that THC can be passed on to infants through breastmilk, but there is limited information about the effect this may have on infants and their development. Similarly, there is limited information about the effect of second-hand cannabis smoke on infants. Given an absence of definitive data showing a lack of harm, ACOG and AAP discourage cannabis use during lactation.1,2
Studies have shown that THC can be detected in the breastmilk of lactating mothers. A 2018 study detected THC in 34 (63%) of 54 samples of breastmilk from women who reported cannabis use, up to 6 days after last reported cannabis use.10 Another 2018 study showed inhaled THC transfer in breastmilk among eight mothers who were regular cannabis consumers, 2-5 months postpartum, and exclusively breastfeeding their infants.11 Subjects discontinued use for 24 hours prior to inhalation of 0.1 g cannabis (23.18% THC), with breastmilk samples collected 20 minutes and one, two and four hours afterwards. THC was detected at all time points, with infants estimated to ingest a mean of 2.5% of the maternal dose (range 0.4-8.7%, average of 8 μg/kg per day).
A prospective observational study of seven women who delivered between 2016-2019 found that THC persisted in breastmilk for more than five weeks despite abstaining from cannabis use after delivery, emphasizing the importance of both early and postpartum avoidance of cannabis exposure.12 THC was detectible in all breastmilk samples throughout the study, with median concentration levels of 3.2 ng/mL within one week postpartum, 5.5 ng/mL at two weeks, and 1.9 ng/mL at six weeks. The estimated half-life of THC in breastmilk in these seven women was 17 days, with a projected time to elimination of more than six weeks.
Regarding the effects of maternal cannabis use during lactation on early infant development, a 1990 study observed that of 136 breastfed infants, a group of 17 subjects with 15-30 days of exposure to cannabis during the first month of lactation exhibited decreased motor development on the Bayley Scales of Infant Development (BSID) compared to matched controls (difference of 12 points).13 However, this difference decreased to five points at three months. Mental development was similar regardless of prenatal or postpartum cannabis use. These findings persisted after controlling for maternal smoking, drinking, and cocaine use during pregnancy and lactation. The authors note that cannabis exposure in the first trimester may have confounded the association between cannabis exposure during lactation and infant outcomes.
A 1985 study examined the effect of cannabis use on birth as well as postnatal outcomes. Of 756 participants, 257 self-reported cannabis use.14 There was no observed associations between cannabis exposure postpartum and motor and mental skills using the Brazelton scale. At one year, there continued to be no association between development and cannabis use.
Overall, the results of studies on the effects of postnatal cannabis use are heterogenous and limited. It should also be acknowledged that a common limitation among these studies is inadequate data on the dosage, frequency, and route of cannabis consumption and a reliance on self-reported data and urine tests that may not accurately capture the exposure to cannabis. However, the presence of data that suggest potential harmful effects, in the absence of definitive data to show otherwise, has led to the recommendation that mothers be encouraged to discontinue all cannabis use during lactation.
References
- Committee Opinion No. 722: Marijuana Use During Pregnancy and Lactation. Obstet Gynecol. Oct 2017;130(4):e205-e209. doi:10.1097/aog.0000000000002354
- Ryan SA, Ammerman SD, O'Connor ME. Marijuana Use During Pregnancy and Breastfeeding: Implications for Neonatal and Childhood Outcomes. Pediatrics. Sep 2018;142(3)doi:10.1542/peds.2018-1889
- Mato S, Del Olmo E, Pazos A. Ontogenetic development of cannabinoid receptor expression and signal transduction functionality in the human brain. Eur J Neurosci. May 2003;17(9):1747-54. doi:10.1046/j.1460-9568.2003.02599.x
- Baglot SL, VanRyzin JW, Marquardt AE, et al. Maternal-fetal transmission of delta-9-tetrahydrocannabinol (THC) and its metabolites following inhalation and injection exposure during pregnancy in rats. J Neurosci Res. Mar 2022;100(3):713-730. doi:10.1002/jnr.24992
- Bailey BA, Wood DL, Shah D. Impact of pregnancy marijuana use on birth outcomes: results from two matched population-based cohorts. J Perinatol. Oct 2020;40(10):1477-1482. doi:10.1038/s41372-020-0643-z
- Luke S, Hobbs AJ, Smith M, et al. Cannabis use in pregnancy and maternal and infant outcomes: A Canadian cross-jurisdictional population-based cohort study. PLoS One. 2022;17(11):e0276824. doi:10.1371/journal.pone.0276824
- Klebanoff MA, Wilkins DG, Keim SA. Marijuana Use during Pregnancy and Preterm Birth: A Prospective Cohort Study. Am J Perinatol. Aug 2021;38(S 01):e146-e154. doi:10.1055/s-0040-1708802
- Ko JY, Tong VT, Bombard JM, Hayes DK, Davy J, Perham-Hester KA. Marijuana use during and after pregnancy and association of prenatal use on birth outcomes: A population-based study. Drug Alcohol Depend. Jun 1 2018;187:72-78. doi:10.1016/j.drugalcdep.2018.02.017
- Shi Y, Zhu B, Liang D. The associations between prenatal cannabis use disorder and neonatal outcomes. Addiction. Nov 2021;116(11):3069-3079. doi:10.1111/add.15467
- Bertrand KA, Hanan NJ, Honerkamp-Smith G, Best BM, Chambers CD. Marijuana Use by Breastfeeding Mothers and Cannabinoid Concentrations in Breast Milk. Pediatrics. Sep 2018;142(3)doi:10.1542/peds.2018-1076
- Baker T, Datta P, Rewers-Felkins K, Thompson H, Kallem RR, Hale TW. Transfer of Inhaled Cannabis Into Human Breast Milk. Obstet Gynecol. May 2018;131(5):783-788. doi:10.1097/aog.0000000000002575
- Wymore EM, Palmer C, Wang GS, et al. Persistence of Δ-9-Tetrahydrocannabinol in Human Breast Milk. JAMA Pediatr. Jun 1 2021;175(6):632-634. doi:10.1001/jamapediatrics.2020.6098
- Astley SJ, Little RE. Maternal marijuana use during lactation and infant development at one year. Neurotoxicol Teratol. Mar-Apr 1990;12(2):161-8. doi:10.1016/0892-0362(90)90129-z
- Tennes K, Avitable N, Blackard C, et al. Marijuana: prenatal and postnatal exposure in the human. NIDA Res Monogr. 1985;59:48-60.
