We continue to see more and more women of reproductive age using marijuana in various forms.  According to research published in the Journal of the American Medical Association, there has been a significant increase in the use of marijuana among pregnant women over the last decade.  Among all pregnant women, the prevalence of marijuana use increased from 2.37% in 2002 to 3.85% in 2014. Marijuana use was the highest in women aged 18 to 25 years, with past-month prevalence reaching 7.47% in 2014.

Despite the relatively high prevalence of its use in pregnant and postpartum women, we have relatively little data on the safety of cannabis in this population.  According to a recent study, low levels of delta-9-tetrahydrocannabinol (THC), the main psychoactive component of cannabis, can be detected in the breast milk of mothers who use it.

This study analyzed breast milk samples from eight mothers who regularly consumed cannabis.  They were between 2 and 5 months postpartum and were exclusively breastfeeding their infants. After discontinuing cannabis for at least 24 hours, they obtained a baseline breast milk sample.  After smoking a preweighed, analyzed, and standardized strain of cannabis, samples of breast milk were collected at 20 minutes and at 1, 2, and 4 hours.

Delta-9-tetrahydrocannabinol (THC) was detected in the breast milk at low concentrations at all time points. THC was transferred into mother’s milk such that exclusively breastfeeding infants ingested an estimated mean of 2.5% of the maternal dose (range 0.4-8.7%). The estimated daily infant dose was 8 micrograms per kilogram per day.  (Just to give you a sense of dose, a typical joint contains 20 mg of THC. If the entire joint is consumed by somebody weighing 60kg, the delivered dose would be around 300 microgram per kilogram.)

While this preliminary study demonstrated low levels of exposure to THC is breast milk, it did not provide any data on the long-term outcomes of these children.  Thus far few studies have looked at the outcomes of children exposed to THC during pregnancy and/or through breast milk.  One of the challenges in gathering data regarding the effects of THC on the developing brain is that it may be difficult to distinguish the effects of THC from other exposures.  For example, women who use cannabis during the perinatal period are more likely to use tobacco and other substances. Furthermore, using cannabis may affect or compromise a woman’s ability to parent, and that may have downstream effects on the child’s development.  

One of the things that concerns me the most is that various research studies have demonstrate that, while the adult brain seems to suffer few long-term effects as a result of cannabis exposure, the developing brain is particularly vulnerable to the deleterious effects of marijuana exposure. Adolescents and young adults who are persistent users exhibit lower psychological functioning and diminished IQ. Studies looking at the effects of marijuana exposure on infants have yielded conflicting results.

While marijuana is viewed as a safe alternative for the treatment of various maladies associated with the perinatal period, including morning sickness and postpartum depression, there is no data to support the use of marijuana for the management of these conditions.    Given that we know so little about the long-term neurobehavioral effects of exposure to cannabis on the developing brain, ACOG and other professional organizations advise mothers to abstain from marijuana during pregnancy and while nursing.  

Ruta Nonacs, MD PhD


Marijuana and the developing brain (American Psychological Association, 2015)

Prenatal, Perinatal, and Neonatal Exposure to Cannabis (National Academies of Sciences, Engineering, and Medicine, 2017)

Baker T, Datta P, Rewers-Felkins K, Thompson H, Kallem RR, Hale TW.  Transfer of Inhaled Cannabis Into Human Breast Milk.  Obstet Gynecol. 2018 May;131(5):783-788.

Miller, CW. Marijuana Use and Breastfeeding. Clinical Lactation, 2012; 3: 102-107.


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