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Home » Marijuana and pregnancy – again hitting that bong of science

Marijuana and pregnancy – again hitting that bong of science

Last updated on October 1st, 2020 at 12:43 pm

Editor’s note–this article has been updated and included into a multi-part series on marijuana and medicine. Check it out there. 

As I have written previously, consumption of and growing marijuana should be completely decriminalized. And the laws need to be rewritten, not in the haphazard way it is now, but with protection and respect of rights of people to consume or grow (for personal use) cannabis. The criminal prosecution of marijuana use and distribution is a ridiculous waste of public resources.

The criminalization of marijuana has caused the growth of drug cartels that threaten the survival of Latin American democracies. And it has caused damage to delicate environments in pristine wilderness in the western USA where illegal marijuana farms use chemicals, human waste and water diversion to destroy the forest.

I could go on, but marijuana laws are simply unsupportable by any stretch of the imagination–the laws waste money and harm citizens.

That being said, it doesn’t mean that cannabis is completely safe. Or that the guy driving his car next to me or a surgeon about ready to slice into my abdomen or the pilot of the jet I’m boarding should be high.

Marijuana should be regulated and taxed like any other product in the class, such as alcohol and cigarettes. It’s a reasonable system where people can enjoy their weed, but it is regulated to prevent harm to others.

Overstating the value of marijuana


It’s clear that the  “pro-marijuana” lobby is promoting some unsupported science to make a case that marijuana can be useful to citizens. This is exactly the same kind of methodology used by the pro-cigarette lobby in the 1950’s and 1960’s when the vast weight of evidence began to show that smoking tobacco was causally linked to certain cancers and other health issues.

As of today, there’s no evidence that smoking pot will cure or prevent cancer. There’s no evidence that it prevents or reverses wasting syndrome from cancer treatments. There’s little evidence that it has any usefulness in ameliorating symptoms of neurodegenerative conditions. Some of the claims are based on animal studies, which, to be frank, rarely become clinically significant.

What really is troublesome is that there’s a belief that even if cannabis isn’t useful in curing cancer, “it is completely safe.” There actually seems to be evidence that smoking marijuana may be no different in lung cancer risk, which is biologically plausible since lung cells tend to be extraordinarily sensitive to environmental hazards.

Claims about marijuana and pregnancy


Recently, I was pointed to some “pro-marijuana” websites that essentially claim that smoking cannabis was safe during pregnancy. I was flabbergasted.

The pro-marijuana lobby group, NORML (the National Organization for the Reform of Marijuana Laws), published an article in 2010, that claimed:

The Occasional Toke: Safe for Moms or Not?–Unfortunately, there is not a definitive answer to this question available at this time. Nevertheless, with a reported three percent of US women of reproductive age reporting that they occasionally use marijuana, it may be arguable that potential pre-natal and post-natal dangers posed by maternal pot use – particularly moderate use – are rather minimal, especially when compared to the in utero exposure of alcohol and tobacco.


The article then cites 15 articles as support for their conclusions. But do these articles really imply that marijuana and pregnancy is a safe combination?

Let’s look:

  • Some of the research is dated. It’s not that old research is necessarily bad, but if one is going to make a serious claim that cannabis use is safe, then bring the most modern and best research possible.
  • Three of the articles are published in journals with an impact factor of 0.00, which means that over the past five years, no one cited any article in those journals. Well-done, well-respected research is published in journals with high impact factors and are cited frequently, up to 100 (and even higher) times a year.
  • One of the recent articles, published in the the British Journal of Psychiatry, showed an odds ratio of approximately unity, meaning that there was no increased risk of psychotic behavior in children of mothers who smoked pot. But the article states that there really were insufficient numbers of women who smoked cannabis during pregnancy to determine if there was a possible risk difference depending on which trimester (which is supported by other studies). In other words, NORML used a source which really doesn’t support their case of safety.
  • Another of the articles, published in one of those 0.00 impact factor journals, makes claims about the usefulness of smoking marijuana to reduce morning sickness. However, it was a terrible study (what do you expect for a 0.00 impact factor journal) which accumulated self-reported results without any serious controls, randomization or blinding. Moreover, the study did not examine the effect of the smoking on any parameter of fetal development. I actually found no evidence that the researchers had any kind of ethics review board approval of this research, and the first author is a proponent of herbal medicine, a mostly pseudoscience.
  • The list of research citations is the perfect example of cherry-picking. They find the studies that support their point of view, when real science looks at all the research, ranks them from best to worst, and see where the evidence goes. But we’ll get to that.



The infamous Jamaica study


This study, published in 1991 in a respected journal, Pediatrics, is quoted frequently in support of smoking cannabis during pregnancy. NORML uses it. At least 100 memes I found on the internet mentioned this article.

Essentially, the study compared the outcomes of 24 children born to mothers who “used” marijuana to 20 children whose mother did not. The researchers concluded that “the neonates of heavy-marijuana-using mothers had better scores on autonomic stability, quality of alertness, irritability, and self-regulation and were judged to be more rewarding for caregivers.” Sounds pretty good.


But let’s examine the evidence presented for quality, because that’s what we should do.

  • This study has only been cited by 5 other articles in the 24 years since being published. If this research was so compelling, so critical, it would be repeated in other populations and published in other articles.
  • A population of only 44 children, roughly divided between the user and non-user groups, is too small to make a clinically meaningful conclusion.
  • There were no controls for confounders (like type of family environment, nutrition, other health issues). Of course, controlling confounders is nearly impossible with just an n=44 population size.
  • Another similarly designed study in Jamaica contradicts the results of Pediatrics study. This is why we don’t cherry pick data–we pick the best evidence published in the best journals to form a conclusion.
  • Ironically, one of the 5 articles in 23 years that did cite the Jamaica study, did its own small study comparing non-user and user mothers and neonatal outcome. The authors concluded that “prenatal cannabis exposure was associated with fetal growth reduction. Meconium testing primarily identifies prenatal cannabis exposure occurring in the third trimester of gestation.” Now I think this studied is flawed in the same way as the Jamaica study, but once again those who advocate that smoking marijuana are cherry picking bad articles, while ignoring others that are less supportive of their point of view.

This so-called “Jamaica study” fails to meet the standards of the highest quality of research, and the results have not been repeated. To use it as the basis of a broad claim that marijuana smoking is safe for fetal development does a disservice to pregnant women. This study is scary bad and is not at all useful in supporting a conclusion about the safety of marijuana use and neonatal outcome.

Breast feeding and marijuana


Since apparently some people think that smoking marijuana post-partum is safe, I thought I’d spend a few moments reviewing the best literature (quality of research matters, so if I’m to be accused of “cherry picking,” it’s picking the best quality).

Here’s what some of that top research conclude:

  1. THC can accumulate in human breast milk to high concentrations.
  2. Infants exposed to marijuana through their mother’s milk will excrete THC in their urine during 2 to 3 weeks.
  3. A large review of the scientific literature regarding breastfeeding and neonatal development showed that breastfeeding while consuming marijuana is “dangerous,” while providing plausible connections between cannabis consumption and several neurodevelopmental issues.
  4. One of the best studies, a a meta-review published in the Journal of Perinatology (a newish Nature journal), Cannabis, the pregnant woman and her child: weeding out the myths (I love a good title), concluded that “women who are using cannabis while pregnant and breast feeding should be advised of what is known about the potential adverse effects on fetal growth and development and encouraged to either stop using or decrease their use. Long-term follow-up of exposed children is crucial as neurocognitive and behavioural problems may benefit from early intervention aimed to reduce future problems such as delinquency, depression and substance use.” In other words, there appears to be high quality scientific evidence that there is a link to certain neuro-developmental issues in children who are exposed to cannabis while breastfeeding.

A lot of people advocate for breast feeding because it’s healthier than formula. Without contributing to that particularly divisive discussion, the thought that cannabis (or any other drug such as cigarettes or alcohol) can get into breast milk and harm the child is particularly scary. Not only do we lack any recent high quality evidence that it’s safe, we actually have real high quality evidence that it’s dangerous.

More high quality evidence

It’s time to move away from critiquing research cherry-picked by marijuana advocates to “support” their beliefs, and move toward research that provides evidence that marijuana and pregnancy is a bad combination.

Let’s find the highest quality scientific studies, systematic reviews–then let’s see what they say. I simply searched PubMed for marijuana (or cannabis), pregnancy (or maternal) and review. Then I read the studies in the best journals with the high quality of data.

  1. A systematic meta-review grading the evidence for non-genetic risk factors and putative antecedents of schizophrenia. Authors concluded that “the risk factors (for schizophrenia) with the highest quality evidence, reporting medium effect sizes, were advanced paternal age, obstetric complications, and cannabis use.” This journal has a relatively high impact factor of 5.056. Furthermore, the authors are well published in schizophrenia research and can be considered authorities in the field. The meta review itself is based 24 published studies. This systematic review is a particularly troubling one about the safety of marijuana consumption while pregnant.
  2. Molecular mechanisms of maternal cannabis and cigarette use on human neurodevelopment. This review article described a plausible biochemical relationship between maternal cannabis consumption and behavior issues of children. The authors concluded “the studies reviewed here emphasize the sensitive nature of the prenatal developmental period, during which cannabis and cigarette exposure can set into motion epigenetic alterations that contribute to long-term disturbances in mesocorticolimbic gene regulation, thereby laying a foundation for increased vulnerability to addiction and potentially other psychiatric disorders.” The researchers lay out a solid biochemical connection between cannabis, and its constituent cannabinoids, and neural receptors in the developing fetal brain. This establishes one of the most important factors in biomedical consensus, biological plausibility.
  3. Chronic toxicology of cannabis. This study analyzed 5198 papers, an impressive review. The author concluded that, “Chronic cannabis use is associated with psychiatric, respiratory, cardiovascular, and bone effects. It also has oncogenic, teratogenic, and mutagenic effects all of which depend upon dose and duration of use.” There’s a lot here that has nothing to do with maternal outcome, but “teratogenic” effects is worrisome, since that implies a dangerous effect on fetal development.
  4. Maternal smoking, drinking or cannabis use during pregnancy and neurobehavioral and cognitive functioning in human offspring. This meta review published in a very high impact factor journal (11.075). Anyways, the authors concluded “that prenatal exposure to either maternal smoking, alcohol or cannabis use is related to some common neurobehavioral and cognitive outcomes, including symptoms of ADHD (inattention, impulsivity), increased externalizing behavior, decreased general cognitive functioning, and deficits in learning and memory tasks.” The authors also stated that “exposure to substances such as alcohol, nicotine and cannabis may produce abnormalities in brain development. The behavioral impact of any such abnormalities that might occur depends on other pre- and post-natal factors, which may include genetic vulnerability.”

Conclusions, the TL;DR version


A high level view of what I’ve read about marijuana and pregnancy when I looked through years of research indexed in PubMed led me to a couple conclusions:

  • The most robust research for the actual clinical effects between cannabis and fetal/neonatal outcome has been published over the past 10 years. It shows that there is a link between cannabis use and neurodevelopmental issues.
  • Without showing a true statistical correlation, it appears that most “pro-cannabis” research, which seems to reject a link between the drug and fetal/neonatal outcome, have poorly designed clinical studies with small numbers. And they’re published in the weakest journals.
  • The best evidence, that is the highest quality research published in the highest impact factor journals, strongly suggests (if not concludes) that smoking marijuana during pregnancy reduces neurodevelopmental outcomes for children.
  • But if cherry-picking is the way to go, I could find a handful of poor-quality, unrepeated research to support a belief that consuming marijuana while pregnant (or breastfeeding) is safe. But what we know of many drug’s effects on fetal development (alcohol and cigarettes just to name two), there is a plausible and logical concern about marijuana and the developing fetus.
  • Marijuana and pregnancy (or while breastfeeding) is a bad combination–it is probably not very safe to the fetus or neonate. That’s very clear.

Editor’s note: This article was originally published in December 2014. It has been completely revised and updated to include more comprehensive information, to improve readability and to add current research.

Key citations:


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