With cannabis legalization happening in Canada, many questions about its use and safety are emerging in pregnancy and breastfeeding.  Increasingly in my practice as a Pregnancy and Post-Partum Psychiatrist at Mount Sinai Hospital in Toronto, Canada, women are informing me that they are already using various forms of cannabis during their pregnancy or while breastfeeding.  Although there is no high-quality research on its effectiveness, many pregnant and breastfeeding women believe it may be helping their nausea, anxiety or insomnia.

Woman with insomnia marijuana

The American Journal of Obstetrics and Gynecology published an excellent review article summarizing the studies done to date looking at the effects of cannabis exposure on a developing fetus and breastfed baby.  Key points include:

  • Marijuana crosses the placenta
  • There is uncertainty of effects on perinatal outcomes
  • Possible increased risk of stillbirth
  • Possible increased risk of preterm birth (mixed data)
  • Uncertain effects on offspring
  • Possible adverse effects on neurodevelopment
  • Possible increased risk of fetal growth restriction (mixed data)
  • No established association with specific congenital anomalies

Studies on rodents have shown that cannabis exposure causes changes in dopamine pathways and symptoms of hyperactivity.  Although animal studies cannot be directly extrapolated to humans, research on human fetuses 17-22 weeks exposed to cannabis showed reductions in dopamine receptors in the amygdala, particularly in males, which is concerning.

Breastfeeding risks

The Ottawa Prenatal Prospective Study recruited women in 1978 and examined 180 offspring of primarily middle class, white, low-risk patients in Ottawa, Canada. After age 4, there were differences in behavioral problems and decreased performance on visual perception tasks as well as language comprehension and sustained attention and memory difficulties in exposed children.

“It is important to bear in mind that the average content of THC in the 1970’s was 1-2%. Now it is generally 10 fold that!”

Maternal Health Practices and Child Development Project (MHPCD) from Pittsburgh, examined mostly high-risk, low-income, minority women and their offspring. Maternal use of 1 or more joints per day during the first trimester was associated with decreased verbal reasoning by the age of 6 years. At age 10, exposed children demonstrated decreased attention and more hyperactivity and impulsivity. Academic performance in reading and spelling and by teacher report was worse as well. Again, at age 14, maternal use was associated with lower scores in math, spelling, and reading. There was also an earlier age of onset of substance use in adolescence and greater duration of use than controls, even after considering home environment and parental substance use.

Misinformation is rampant.

In a 2016 study published in the American Journal of Obstetrics and Gynecology, results on an anonymous survey (predominantly white and college-educated), only 49% of people thought that cannabis could pass to a baby.

Much like alcohol and tobacco, just because a cannabis is legal and natural, doesn’t guarantee it is safe for your baby.

Legalization changes usage patterns.

In Colorado, self-reported use in women increased from 4.3% to 7.2% from 2013 (before legalization) to 2014 (post legalization). Usage rates based on actual toxicology screening went from 16.7% to 27.9% over the same time period.

Unfortunately, no safe amount of cannabis use can be recommended at this time in either pregnancy or breastfeeding for a number of reasons:

  • Cannabis use has been shown in a number of studies to potentially cause low birthweight in babies and there is a concerning pattern of altered neurodevelopment with regular maternal use in pregnancy. This may mean a reduction in IQ for young children, difficulties with attention and learning.
  • Endocannabinoids (including THC and CBD) pass to the baby both via the placenta and breastmilk.
  • No safety data exists yet on the effects of CBD use exclusively.
  • Cannabis passes through to breastmilk and can remain there for up to 6 days after the last use with unknown effects on developing babies.
  • Cannabis strength remains highly variable even within the same dispensary and often a very different concentration than labeled. It is uncertain how legalization will impact this as much of the cannabis is already approved in Health Canada licensed facilities.
  • Impurities while smoking or vaping can affect health. Holland is the only country in the world that performs gamma irradiation of cannabinoids in order to remove mold and pesticides.  Some people carry a genetic variant making it difficult for their immune system to clear molds, making smoking or vaping potentially dangerous to a developing fetus, risking exposure to mycotoxins such as Aspergillus.
  • Even if formula feeding, cannabis has potential side effects in some people including: anxiety, paranoia and hallucinations. Cannabis is not a proven treatment for depression or anxiety and can interfere with the effectiveness of antidepressant medications.  It can also be dangerous to drive due to slowed reaction times.


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