What we know about how safe cannabis is for pregnant women and breastfeeding moms

Posted on: 03-24-2019 20:10:51

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Researchers say there is a lack of scientific research when it comes to cannabis and pregnancy. (The Canadian Press)
What we know about how safe cannabis is for pregnant women and breastfeeding moms.
Sarah Konefal of the Canadian Centre on Substance Use and Addiction explains what the research tells us about the safety of cannabis for pregnant and breastfeeding women. 8:39 

While we know a lot about the dangers of drinking alcohol or smoking cigarettes while pregnant, now that it's legal, what about using cannabis? There is much less that we know about what happens to babies when their moms use pot while pregnant or breastfeeding.

This week hundreds of health care professionals are gathering to hear presentations that will look at those questions. Sarah Konefal, a research and policy analyst with the Canadian Centre on Substance Use and Addiction, will be one of the speakers. 

She spoke with the CBC's Conrad Collaco about what we know now about the effect of cannabis on women who are pregnant or breastfeeding. You can read an abridged and edited version of the interview or listen to the full audio interview by hitting the play button above. 

 Sarah Konefal, Canadian Centre on Substance Use and Addiction 



(Canadian Centre on Substance Use and Addiction)


What do we know about using pot while pregnant?

We know from studies that frequent use of cannabis during pregnancy — daily or near daily use — does increase risk of adverse outcomes including risk for low birth weight as well as adverse effects on cognition and behaviour in children and adolescents that persists to early adulthood. This contributes to poor academic achievement.

This risk is independent of alcohol or tobacco use. It does hinge on smoking cannabis. We don't know too much about what happens if a pregnant woman is using via the other ways of consumption. We also don't know too much about risks that are specific to breastfeeding. If a woman is using cannabis while breastfeeding it's most likely she was using cannabis while pregnant. We do know that THC, one of the important psychoactive compounds of cannabis does get into the breast milk. It is transferred to the infant, metabolized and excreted, so there is definitely the potential for that affecting brain development. 

There's really no evidence that there is a safe amount of cannabis to consume and really if you want to be on the careful side that's what you should aim for.- Sarah Konefal, Canadian Centre on Substance Use and Addiction

How do the effects of cannabis compare with the effects of alcohol and tobacco?

The research so far indicates that there's less risk. Some of that is due to a thinner research base. The strong effects are contingent on the frequent, heavy use of cannabis. Towards that end of the spectrum you can get some of these cognitive and behaviour outcomes that can echo, to a lesser degree, what happens when a mother consumes alcohol during pregnancy. 

What qualifies as heavy use versus occasional use? 

One of the issues with the research is inconsistent quantification of cannabis use. That's not just specific to cannabis use during pregnancy. For research that looks at the effects of cannabis on other health issues like mental health there is inconsistency in how heavy use is quantified. That contributes to the variability of the findings.

It makes it difficult for researchers to pool together results from different studies. Generally, heavy use refers to almost daily to more than one joint per day, for example. There's little evidence to suggest occasional use — say using once per month, for example — results in these stronger adverse outcomes.

What advice do you have, based on the research, for women who are pregnant or breastfeeding?

My two main messages would be — this is what the health care providers are going to say — there's really no evidence that there is a safe amount of cannabis to consume and really if you want to be on the careful side that's what you should aim for.

If someone's using cannabis during pregnancy there might be a bunch of other factors accompanying that. Just telling someone not to use might not be the most effective approach. Having a harm reduction approach and trying to cut back on use, if possible, is the most viable option.  

What are family doctors and pediatricians telling mothers about cannabis use?

If you look at the Canadian Paediatrics Society or the Society of Obstetricians and Gynaecologists Canada, their message is that there is no safe amount. There is enough research to indicate there is a potential for risk. Not just the potential. There are actual risks, the research shows. 

Why is there so little research on cannabis and pregnancy?  

There is the legalization aspect. Cannabis was illegal for a long time. That made it difficult for researchers to gain funding and gain access to cannabis for research purposes. There is some evidence leading up to legalization that there was a perception that because it was legal it must be safe, or because it is natural it is a safe substance.

A study in 2012 looked at perceptions of pregnant mothers and found that while 70 per cent identified alcohol as being a risky substance to use, only two percent identified cannabis as a risky substance. 

It's a challenging substance to research as well because there are differences in strains. You can have one strain that is very high in THC and very low in other cannabinoids and vice versa. That has made it difficult to pull together a bunch of studies on cannabis and find a common theme or conclusion.

Is there any difference for pregnant women if the cannabis is smoked or eaten?

There's not yet any information available on that. There has been a shift in research to look at the different modes of consumption. In the past it was focused on smoking cannabis. Now we are aware that is not going to capture all the information we need to capture. 



Conrad Collaco


Conrad Collaco is a CBC News producer for CBC Hamilton with extensive experience in online, television and radio news. Follow him on Twitter at @ConradCollaco, or email him at