With the legalization of cannabis in many states, discussion surrounding the safety of cannabis during pregnancy is becoming more prevalent. Sure, the herb can be useful when treating morning sickness and anxiety, but how much, if any is safe?

Trends in Prenatal Cannabis Use

According to an article published in Experimental Biology, legalization has increased dramatically the number of pregnant women reportedly using cannabis. From 2002 to 2014, cannabis use increased by 62% for pregnant women. [note]https://www.sciencedaily.com/releases/2019/04/190409135933.htm[/note] This statistic may sound drastic; however, other studies show how little the plant is actually used by pregnant women that self-report. Reviewing data from the Kaiser Permanente Northern California, researchers found from 2009 through 2016, prenatal cannabis use did increase in California from 4.2% to 7.1%. [note]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5769923/[/note] Of course, the data is limited by self-reporting tendencies and could underestimate the actual percentages.

There are so many articles with varying results on the effects of cannabis use during pregnancy. Often, these studies include other narcotics, such as cocaine. The women included in such studies may have poorer diets and habits as a result, rather than someone using cannabis for medicinal purposes or on occasion. There’s a lot of research; however, it is very limited, and much of it from the 1980s when cannabis was illegal. As one study notes, “There is a lack of quantification of marijuana exposure by the trimester of use and a lack of corroboration of maternal self-report with biological sampling, which contributes to the heterogeneity of study results.”[note]https://www.sciencedirect.com/science/article/abs/pii/S0002937815005013[/note] Hopefully, this will help you wade through some of the findings.

Is Cannabis Safe to Use While Pregnant?

The active psychoactive ingredient THC has been found in breastmilk and is known to “rapidly” cross through the placenta to the fetus. A study conducted in 1987 with rhesus monkeys in the late-term of pregnancy is often cited to warn of the risks of prenatal cannabis use.[note]https://www.ncbi.nlm.nih.gov/pubmed/2820086[/note]

Low Birth Weight, Gestational Length and Cannabis Use

Another study conducted in Great Britain involved 12,000 women who self-reported cannabis use both before and after pregnancy. This large study found “the use of cannabis during pregnancy was not associated with increased risk of perinatal mortality or morbidity in this sample.” Researchers did; however, discover that mother’s who used cannabis at least once a week while pregnant gave birth to babies with smaller birth weights. Specifically, cannabis-using mothers gave birth to babies that were 90 gram lighter than non-users. [note]https://obgyn.onlinelibrary.wiley.com/doi/full/10.1111/j.1471-0528.2002.01020.x[/note] A different study published in the New England Journal of Medicine found prenatal cannabis use resulted in babies weighing 79 grams less. [note]https://www.nejm.org/doi/full/10.1056/NEJM198903233201203[/note]

Contradicting the above studies, a 1984 article in the American Journal of Obstetrics and Gynecology followed women that used cannabis six or more times per week and found no difference in birth weight. Instead, this study found cannabis caused the gestational length to be reduced by 0.8 of a week. [note]https://www.sciencedirect.com/science/article/abs/pii/S0002937884801039[/note] A large study conducted in Ontario, Canada of 661, 617 women self-reporting cannabis use found it “was significantly associated with an increased risk of preterm birth”. [note]https://jamanetwork.com/journals/jama/article-abstract/2736583[/note]

Weakened Immune System and Cancer

A more recent study published on February 2019 in the peer-reviewed Cellular and Molecular Life Sciences found the most severe results of prenatal cannabis use.

In addition to significant neurological effects, cannabinoids can trigger robust immunomodulation by altering cytokine levels, causing apoptosis of lymphoid cells and inducing suppressor cells of the immune system. Profound effects of cannabinoids on the immune system as discussed in this review, suggest that maternal exposure during pregnancy could lead to dysregulation of innate and adaptive immune system of developing fetus and offspring potentially leading to weakening of immune defenses against infections and cancer later in life. Emerging evidence also indicates the underlying role of epigenetic mechanisms causing long-lasting impact following cannabinoid exposure in utero.

Cannabinoid exposure during pregnancy and its impact on immune function.

Behavior, Learning, and Memory Problems with In Utero Cannabis Use

Another 2019 study published in Experimental Biology found that in utero cannabis use affected children’s memory, behavior, and learning abilities by changing the “intricate connections in nerves in the hippocampus, the brain’s center for learning and memory.” It’s important to note that this study was conducted on rats and a synthetic chemical was used, not cannabis itself, it imitate heavy use. The synthetic cannabis resulted in reduced synapse connections in the hippocampus. The study suggests this effect may be counteracted to allow for the plant to be used safely in pregnancy. [note]https://www.sciencedaily.com/releases/2019/04/190409135933.htm[/note]

Are There Any Benefits to Prenatal Cannabis Use

Just a reminder, any medical decisions you make while pregnant should be discussed with your doctor and/or midwife. In my personal experience, my midwives recommendations varied. They told me of one client they refused to work with because she would not quit using cannabis. In other cases, they recommended light use, not long term, for those with severe morning sickness.

The truth is, we just don’t know if it is safe. The medical community has not wavered in warning that cannabis use is not recommended in utero, including CBDs. There are problems with all of the studies thus far, many of which are 30 years old, and clinical trials are needed. [note]https://www.whattoexpect.com/pregnancy/marijuana/[/note][note]https://www.leafly.com/news/health/cannabis-and-pregnancy-what-does-the-science-say[/note]

Just because cannabis is natural, it may not be benign for your unborn child. That being said, the side effects of other prescription drugs used to treat anxiety and morning sickness may be just as detrimental.

Take for example Diclegis, the only FDA approved medicine for morning sickness. The manufacturer claims the drug is safe for your baby but warns not to take it while breastfeeding. The drug manufacturer warns, “Diclegis^® can pass into your breast milk and may harm your baby. You should not breastfeed while using Diclegis^®.” Additionally, they warn, “Diclegis^® may cause an incorrect positive result for urine drug screening tests for methadone, opiates and PCP.”[note]https://www.diclegis.com/en/what-is-diclegis[/note]

Other problems with Diclegis is that the industry-backed clinical study done to prove its safety was conducted in the 1970s and never published in a peer-reviewed scientific journal (all of the studies referenced above were regarding cannabis use). The study is also missing data.

Futhermore, most FDA approved drugs do not involve pregnant women in their clinical studies. CNN reports:

Due to this lack of research, less than 10% of medications approved by the FDA since 1980 have enough data behind them to determine their risk for birth defects, according to a 2011 study published in the American Journal of Medical Genetics.

Morning sickness drug’s efficacy called into question

Diclegis is a rebranded version of Bendectin, a drug that was voluntarily removed from the market due to lawsuits claiming it caused birth defects.

Furthermore, Diclegis has not been studied with women who experience severe morning sickness. Cannabis may be a safer option in these cases, yet there is not enough research to support one way or another.

Clearly there are drawbacks to studies based on self-reporting cannabis use during pregnancy. Other studies that analyze urine involve relatively small sample sizes. An Australian 2012 study sums up the inconsistencies evident in the studies’ methods as reported by Leafly:

The findings of this study are consistent with previous research, which has suggested that smoking cannabis during pregnancy may lead to lower birth weight, increased rate of premature birth, and shorter birth length. However, our data are inconsistent with findings of studies that have not found a significant association between cannabis use in pregnancy and birth outcomes. The existing discrepancy between the findings might be due to the difference in the study design and assessment of cannabis use (e.g., retrospective vs. prospective) or level of adjustment for confounders. 

Consuming Cannabis During Pregnancy: Here’s What the Science Says

Cofounders refers to a problem we mentioned earlier that it’s difficult to separate cannabis use in the studies from alcohol, tobacco, or other drugs like cocaine. Results are inconsistent and unreliable, especially when studies rely on self-reporting and combine other known harmful substance.

So for now, the precautionary principle rules when it comes to cannabis and pregnancy, which seems wise until further research is conducted; however, perhaps the risks are comparatively fewer than prescription drugs for morning sickness.

If you suffer from severe morning sickness, talk to your midwife and/or doctor about remedies. Do your own research so you can have an intelligent conversation and ask poignant questions.