Can Cannabis Be Used During Pregnancy?

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"With more women turning to cannabis use during pregnancy its a good time to look at the science."
Cannabis-and-pregnancy

One of the major focuses of research lately has been on how cannabis use during or after pregnancy affects newborns. This is, of course, an important field of study as with alcohol and opioid use the effects can be great, and permanent. Although there are many proposed explanations and the relative impact of various causes is not yet well understood, the rate of developmental disabilities in children are rising. Following the precautionary principle, of course all pregnant women should take care to remain healthy and not consume any substances that may harm their babies, but what about medical cannabis patients?


Many women experience severe nausea and vomiting during pregnancy, which can lead to a multitude of issues at home and work, and in the most severe cases can led to hospitalizations and affect he development of the fetus. Increasingly, women are being told that cannabis is a safe alternative to pharmaceuticals in addressing nausea and vomiting during pregnancy. But is it really safe? In today’s article we will look at the studies that have been done so far, and attempt to quantify the impact that cannabis consumption could have on a developing baby, or a breastfeeding newborn. We will also explore many questions that cannabis users who think they may become pregnant might have.

Study Finds That THC and CBD Could Disrupt Fetal Development by Pregnant Women

Why are pregnant women using cannabis?

As noted in an article published in August of this year, most of the animal or lab studies on pregnancy and cannabis use conclude with the statement that “further research is required.” However, this research is very difficult to perform, as ethics rules generally prevent any researchers from administering a Schedule I Controlled Substance to a pregnant woman. Doing so would be met with harsh criticize, as it is unethical to do anything which could harm an unborn child permanently. These rules where solidified after the 1950’s incident involving the sedative thalidomide, which caused major birth defects and developmental disorders in the children of mothers who had taken it.

Ethics and safety issues caused the field to largely stall out, until 2013 when the FDA approved the drug Diclegis. This drug however is expensive and not largely effective, leading many women to turn to the drug Ondansetron, even though it is not FDA approved for pregnant women due to some incidences of birth defects.

So, many women turn to cannabis as a safe, natural alternative. This has increased following the FDA approved cannabis and an antiemetic for cancer patents in 1996, and is highest among women with depression. By 2006, a study in Canada had found that found that 65% of pregnant women had used cannabis for nausea and vomiting. Furthermore, 92 % of them said it was 'extremely effective' or 'effective' at addressing nausea and vomiting symptoms. The most common routes of cannabis consumption are smoking (42%), edibles (16%), vaping (16%), and lotions (5%).

A large study from this year, found that number was less, at 11.3%., with 4.8% saying they would continue to use cannabis while breast feeding. In the UK, it was reported that the rate had gone down from 15.8% to 2.5% over the period from 1999 to 2009. So, although some studies say that the rate is increasing, it is hard to see that in the data.

Studies have shown that 99% of women in Canada understand that the cannabis may be transmitted by blood or milk to the fetus. In a 2020 survey of Canadian mothers, 22.6% believe there is no harm or are unsure of the harm to the fetus during pregnancy, and 30.4% believe the same regarding breastfeeding. That same study concluded that it was clear that parents lack information about cannabis use during pregnancy and breastfeeding.

Study-says-women-who-use-marijuana-regularly-have-better-sex

What are the effects of using cannabis during pregnancy?

Throughout the 1990’s and early 2000’s a wealth of studies was conducted which pointed to cannabis use causing low birth weight and preterm delivery, as well as a long list of rare but serious effects, including death or stillborn. The main cannabinoid in cannabis, THC does pass easily through the placenta membrane, and smoking cannabis increases blood carbon monoxide levels and may lead to reduced gas exchange with the fetus.

Studies showing no negative effects

A 2016 meta-review looked at all these studies and adjusted for tobacco use and other confounding factors. Before adjustment, the pooled data from more than 31 studies showed that there was an increase in incidence of low birth weight from 10.4% to 15.4%, and an increase in preterm births from 9.6% to 15.3%. However, once the data was adjusted for tobacco use and other confounding factors, than there was no significant increase in adverse neonatal outcomes. Meaning that it was likely that all of the negative effects shown in previous studies had been wrong as they had not controlled for tobacco use, which is likely what led to the observations.

A deeper study also from this year, found that the negative effects of cannabis where significant only in heavy daily users, whereas there were no observed increases in disorders or developmental problems in infrequent users. So, as we have seen above, there is currently little to no consensus on the effects that cannabis use has on neonatal development or development later in life.

Studies which disagreed

Although that study above was the largest meta-review to date, it did not end the debate. In 2020 another review claimed much to the opposite. Citing just one source, the review stated that “we know prenatal cannabis ingestion has been associated with anemia in the mothers as well as low birth weights, greater risk of preterm and stillbirths, and increased need for neonatal intensive care unit admissions.” It went on to point out that there are also long-term implications, including higher rates of impulsivity, delinquency, learning and memory impairment as well as executive function deficits (again citing a single study). Despite the lack of references to other studies, or to the 2016 meta-review mentioned above, this paper recommended that all pregnant women should be screened for drugs, and that policy should be extended to all areas of medicine. So, as you can see, the issue is far from solved, and women can be forgiven for feeling confused when presented with these opposing conclusions.


Another study, published in August of this year looked at existing birth data from 2007-2012. After adjusting for cofounding factors and other substance use, it was shown that there was increased hazard of developing several developmental or learning disorders. The hazard ratio for autism spectrum disorder increased by 1.54, meaning that the rate went from 2.42 per 1,000 person-years in the standard population to 4.0 in the cannabis using mother populations. This was also seen for several other disorders, including a increase of 1.35 for intellectual disability and learning disorders, 1.11 for ADHD. Although the author’s concluded these results should be taken seriously, they also stated that the data was not statistically robust, and then empathized that caution should be taken when interpreting the results due to the inability to adjust for all factors, as it was not a controlled clinical trial.

The fact that many of the reviews used to advise pregnant women, as in the 2020 review in the Psychiatric Times mentioned above, are based on very few cherry-picked studies only adds more confusion to the situation. Until actual clinical trials could be carried out, it is very hard to say what the real risks are, and if there is still a perception that those risks are great, then those trials will never be initiated for ethical reasons. So, what are pregnant mothers who worry about the side effects of pharmaceutical drugs to do?

Use of Marijuana During Pregnancy Can Negatively Affect Fetal Development

A bit of common sense in the debate

After extensive research, we came across a paper in the Journal of Preventative Medicine which may help to advise women considering cannabis use during pregnancy. The authors of the study recognized that cannabis use is common and increasing among women, and will continue to do so as liberalization of the plant continues globally. And, although there is theoretical potential and some limited data to show that it may interfere with development, the largest studies to date have failed to show any significant long-term or long-lasting effects.

The study went on to criticize most previous studies, recognizing that results are generally over or under-stated, and recognized that the legal status of a substance is not a reason to assume it is safe or dangerous. As such, it points out that in many states the punitive damage to the mothers (fines, separation, incarceration) have a larger effect on the children than the cannabis use itself.

So, although most countries' governments would rightly advise that “women who are thinking about becoming pregnant, are pregnant, or breastfeeding should abstain from using cannabis.” As with alcohol and tobacco, there is no reason for the punitive punishments that are currently given to cannabis-using mothers when the effects of legal alcohol and tobacco are a much greater risk to their babies. If you do decide to use cannabis during pregnancy or breastfeeding, be sure to talk to your doctor so that they may monitor for any ill effects and explain all the risks.

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chadscott@vapebiz.net
Chad Scott is a freelance science writer who specializes in the field of cannabis. He spent over a decade living in Thailand. He was diagnosed with Acute Myeloid Leukemia while living in Thailand in 2016. Upon diagnosis, Chad immediately began chemotherapy at a rural hospital in the country. He continued to use cannabis oil throughout his chemotherapy treatments for almost 1 year, and never again experienced any nausea or vomiting, and was able to sleep and eat normally. From his personal experiences, he has become an advocate for medical cannabis and believes that all cancer patients should have the right to access this natural medicine if they so choose.

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