Marijuana crosses the placenta and appears in breast milk, with emerging evidence linking prenatal exposure to fetal growth restriction, possible stillbirth and preterm birth, and neurological development problems in children.
Read this if you are pregnant, planning pregnancy, or breastfeeding and use or are considering using marijuana.
3-30% of pregnant women use marijuana depending on population
What the researchers found
This review examined the evidence on marijuana use during pregnancy and lactation, noting that 3-30% of pregnant women use marijuana depending on the population studied.
THC freely crosses the placenta and is found in breast milk. The review identified several potential adverse outcomes: fetal growth restriction, possible associations with stillbirth and preterm birth, and emerging evidence of neurological effects including hyperactivity, poor cognitive function, and changes in dopamine receptors in exposed children.
However, the evidence was far from uniform. Most studies were confounded by concurrent tobacco and other drug use, sociodemographic factors, lack of trimester-specific exposure data, and reliance on self-report without biological verification.
Why it matters
As marijuana legalization expands, more women may use it during pregnancy, potentially unaware of risks. This review highlighted both the potential harms and the significant gaps in evidence that make definitive risk counseling difficult.
The numbers in context
Prevalence of use: 3-30% across populations; THC crosses placenta and enters breast milk; associated outcomes: fetal growth restriction, possible stillbirth, preterm birth, hyperactivity, cognitive effects
How the study worked
Narrative review of published literature on marijuana use in pregnancy and lactation, with emphasis on perinatal outcomes and fetal neurodevelopment. Published in a leading obstetrics journal.
What this study cannot tell us
Most existing studies have significant confounding from tobacco and other substance co-use. Self-reported marijuana use is unreliable. Lack of dose quantification by trimester. Difficulty isolating marijuana effects from sociodemographic risk factors.
How to read the evidence
Comprehensive review in a major obstetrics journal, but hampered by the limitations of the underlying studies, which are heavily confounded.
When this study was published
Published in 2015. Cannabis potency has continued to increase, and more research on prenatal exposure has been published.
The bigger picture
Contemporary marijuana is substantially more potent than the products studied in the 1980s when much of the foundational research was done. This means older studies may underestimate risks, and new research with current products is urgently needed.
Questions still open
- What are the effects of today's higher-potency marijuana on fetal development? Are there critical windows of vulnerability during pregnancy? How long does THC persist in breast milk after use? Do CBD-only products carry the same risks?
Common questions
Is marijuana safe during pregnancy?
Does THC get into breast milk?
Read the original research
Marijuana use in pregnancy and lactation: a review of the evidence.
American journal of obstetrics and gynecology, 213(6), 761-78
Citation
Metz, Torri D; Stickrath, Elaine H. (2015). Marijuana use in pregnancy and lactation: a review of the evidence.. American journal of obstetrics and gynecology, 213(6), 761-78. https://doi.org/10.1016/j.ajog.2015.05.025
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