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Ira J. Chasnoff, M.D.

Ira J. Chasnoff M.D.

Medical Marijuana and Pregnancy

Should a doctor do a pregnancy test before prescribing marijuana to a woman?

Any long-term readers of this blog saw the rash of criticism I received regarding my two blog entries regarding marijuana use in pregnancy. But as an increasing number of states pass or consider medical marijuana laws, we need to re-visit the issue. Since much of the objection was based in individuals’ perceptions of the research literature, I decided to perform a comprehensive review of the neurophysiology, obstetric, pediatric and child development literature. The resulting article was published this month in The American Journal of Obstetrics & Gynecology. The article addresses the issue of marijuana use in pregnancy and raises the question: If a woman of childbearing age requests a prescription for marijuana, should the physician obtain a pregnancy test before writing the prescription?

Marijuana is highly fat soluble and crosses the placenta and the blood brain barrier with ease, accumulating in fetal tissues, particularly the brain. Recent studies from Colorado document increasing concentrations of THC, the active ingredient in marijuana, in exposed newborn infants’ first stool. In the adult brain, THC interferes with the nervous system’s signaling system, interfering with the ability to regulate motor control, memory, and other brain functions. Because vulnerable parts of the embryo’s nervous system are developing as early as 16-22 days after conception, it makes sense that a large study conducted by the US National Birth Defects Prevention Center documented a significantly increased risk for anencephaly (babies born missing the front part of their brains) when the fetus is exposed to marijuana during this period. Exposure to marijuana later in pregnancy affects the development of the fetus’ neurotransmitter systems, affecting communication between nerves. Exposure to marijuana around 18-22 weeks of gestation affects communication systems within the developing amygdala and nucleus acumens, affecting cognitive and emotional functioning in the child. The resulting deficits in neurobehavioral functioning that have been observed in multiple studies in newborns exposed to marijuana reflect impaired regulatory control: irritability, tremors, and poor habituation; difficulty with arousal and state regulation; and sleep disturbance. Although two studies indeed have found no neurobehavioral differences between marijuana-exposed and non-exposed infants in the early neonatal period, these two studies differed from all the others due to sociocultural differences as well as varying statistical treatment of the different confounding factors.

Long-term studies of children prenatally exposed to marijuana once again are consistent with THC’s action on the developing fetal brain, with significant deficits in aspects of cognitive functioning, focusing primarily on memory, behavioral regulation, and executive functioning, an aspect of regulatory control that is key to learning and to managing behavior. Finally, a study of functional MRIs in a group of 18- to 22-year old young adults who had been prenatally exposed to marijuana revealed altered neural functioning that impacted short term memory.

Further animal and human studies are needed, but in the meantime, there is certainly enough evidence to suggest that, contrary to popular perception, marijuana is not a “harmless” drug. Thus, as medical marijuana becomes more popular as a method of treatment, the public health system has a responsibility to educate physicians and the public about the impact of marijuana on pregnancy and to discourage the use of medical marijuana by pregnant women or women considering pregnancy.

If you would like a copy of the research article and the complete set of references published in The American Journal of Obstetrics and Gynecology, simply contact me via and I will send it out to you. It is time to set the record straight regarding marijuana’s effects on pregnancy and the developing child.


About the Author

Ira J. Chasnoff, M.D.

Ira J. Chasnoff, M.D., is a Professor of Clinical Pediatrics at the University of Illinois College of Medicine in Chicago. His most recent work is The Mystery of Risk.


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