Does Cannabis Use During Pregnancy Harm your Baby?

Another week, another cannabis study blown out of proportion by the media. “How pot harms your baby’s brain: Smoking cannabis in pregnancy ‘impairs memory, decision-making and personality,’” say the Daily Mail. “Mothers Beware!” yell the Economic Times. But what’s the truth here? To find that out, it helps, as always, to read the actual study yourself.

The basis for these latest scare stories comes from The Netherlands, where scientists led by Dr Hanan El Marroun from Erasmus University Medical Centre have conducted research (published last year, but only just picked up by the press) into the effects of cannabis and tobacco use during pregnancy on child brain development.

The scientists “matched 96 children prenatally exposed to tobacco only (without cannabis) with 113 unexposed control subjects on the basis of age and gender and subsequently selected 54 children exposed to prenatal cannabis (mostly combined with tobacco exposure).” The children were chosen from a previous cohort study – dubbed the ‘Generation R Study’ – in which 9778 mothers with a delivery date from April 2002 until January 2006 were enrolled, and the progress and health of their children monitored from before they were born. The Generation R Study itself is still ongoing.

The purpose of this new study was to look at some of the subjects of Generation R to see what effect, if any, cannabis use by their mothers has had on their brain development. As was rightly reported by most media outlets, it was discovered that cannabis use seemed to correlate with a thickening of the prefrontal cortex, an area of the brain associated with complex cognition, decision-making, and working memory.

As the scientists themselves admitted, though, they had a hard job finding infants who had been exposed to cannabis only – without tobacco – hence the decision to also include a control group of those exposed only to tobacco to give them some idea of the differences between the two. What they found was that whilst cannabis seemed to thicken the prefrontal cortex, tobacco alone appeared to make it thinner. So at first glance it would appear that the headlines are indeed correct.

However, it is not that simple. The study did not find that cannabis exposure had any effect on the total brain volume, grey matter volume, or white matter volume, something which was observed in children exposed only to tobacco. And whilst the scientists made every effort to factor in things such as prenatal alcohol exposure, as well as the subject’s backgrounds and ethnicities, there is as yet – since the subjects are still children – no data on exactly if or how the thickening of their prefrontal cortex has affected their lives. This would of course be near impossible to prove at any rate, given the myriad array of factors at play during childhood and adult life which all have a role in determining where an individual ends up.

That’s not to say that this isn’t something which should be looked into more thoroughly, of course, but as Dr Marroun pointed out, “We have to be careful interpreting the results of the current study.” This statement echoes the final line of the study itself, which states that “More research is needed to explore the causal nature of this association.”

It’s clear then that as usual, the findings of this study have been somewhat overstated by the more hysterical sections of the press. Whilst the smoking of tobacco and cannabis should probably be avoided during pregnancy, there’s no need yet to presume that your child is going to be somehow brain damaged if you happen to be a cannabis user. There’s certainly no basis for using this study, which found potentially more significant changes to the brain caused by tobacco, a legal drug, than by cannabis, as a stick to bash legalisation with. The argument simply doesn’t hold up.

Deej Sullivan
Deej Sullivan is a writer and activist from the UK. He regularly writes on drug policy and politics for NORML UK, the UKCSCs, London Real, and his own blog,



  1. Louise Saoirse says:

    Melanie Dreher did a five year study into the use of cannabis during pregnancy. They found that babies scored higher in several areas in the thirty days after birth. A follow up study concluded that there were no differences between the group whose mothers used cannabis, and the control group.

    Mainstream media can’t be trusted to deliver truthful news to people – they have an agenda. Nobody wants to see babies or children being damaged, but the science shows so far that cannabis doesn’t seem to do damage.

  2. Another study which is never mentioned – “Mortality within the first 2 years in infants exposed to cocaine, opiate, or cannabinoid during gestation” published in the Pediatrics journal, is even more of an eye opener. It found a dramatic decrease in the mortality rate of babies born testing positive for cannabis. “A total of 2964 infants were studied. At birth, 44% of the infants tested positive for drugs: 30.5% positive for cocaine, 20.2% for opiate, and 11.4% for cannabinoids…Within the first 2 years of life, 44 infants died: 26 were drug negative (15.7 deaths per 1000 live births) and 18 were drug positive (13.7 deaths per 1000 live births)…The mortality rate among cocaine, opiate, or cannabinoid positive infants were 17.7, 18.4, and 8.9 per 1000 live births, respectively.” However, many of the babies that tested positive for cannabinoids, also tested positive for cocaine and/or opioids. Once they screened the babies for those that only tested positive for cannabinoids and no other drugs (157 babies), the mortality rate was 0.0 per 1000 live births. No, that is not a typo – zero deaths. The other fact that stands out in this study is that the overall drug positive death rate (13.7 deaths per 1000 live births) was lower than the drug negative rate (15.7 deaths per 1000 live births). What would account for this? If you look at the death rate for cocaine (17.7) and opiate (18.4) positive babies, they are higher than the drug negative death rate. Therefore, it seems that cannabis provided some sort of protection for babies exposed to cocaine and opiates (8.9 deaths per 1000 live births). A possible reason why cannabis exposed babies had a much lower mortality rate is because they had a more robust Endocannabinoid System, due to the fact that their mothers consumed cannabis while pregnant.

  3. it must be pointed out that smoking (which means combusting) is the least healthy way to consume cannabis. When you smoke cannabis, the process of combustion creates substances like benzene, carbon monoxide, naphthalene, toluene and polycyclic aromatic hydrocarbons (commonly known as PAHs). But studies have shown that vaporizers greatly decrease these unwanted toxins. Vaporizers don’t combust cannabis, instead they heat the cannabinoids to their boiling point which evaporates them, allowing them to be inhaled. Therefore, it’s recommended that if pregnant women do choose to consume cannabis for medicinal purposes, they should use a vaporizer instead of smoking it.

  4. Pregnancy is experienced differently from mother to mother – some appear to breeze through it (relatively speaking) while for others it’s more of a struggle. In a small percentage of cases, women experience hyperemesis gravidarum which leads to severe nausea and vomiting resulting in weight loss and dehydration, and can endanger the lives of the mother and fetus. Although a certain amount of stress is to be expected during pregnancy, excessive stress has been proven to have negative consequences for the fetus. Simple logic dictates that the worse a pregnant mother feels throughout her pregnancy the worse it is for her fetus and vice versa. The most common sources of discomfort for a pregnant women are: nausea, vomiting, backaches, constipation and lack of sleep. It turns out that, with the exception of constipation, cannabis has an excellent track record of alleviating these symptoms. So it makes sense for pregnant women who are struggling with these issues, to use cannabis to alleviate these symptoms and the stress they cause. This is backed up by survey conducted on pregnant women in Canada: ”While 59 (77%) of the respondents who had been pregnant had experienced nausea and/or vomiting of pregnancy, 40 (68%) had used cannabis to treat the condition, and of these respondents, 37 (over 92%) rated cannabis as ‘extremely effective’ or ‘effective.’” What is perplexing is that currently in the US, women who are suffering from severe nausea and vomiting are prescribed antiemetic off label drugs like zofran, phenergan and compazine. These drugs have numerous potential side effects which can lead to great discomfort. But what is truly shocking, is that these drugs are rated as Category C by the FDA Pregnancy Categories (NOTE – The FDA changed its labeling system in June 2015). Per the FDA, Category C drugs are described as: “Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks”.

  5. Morning sickness is bad, hyperemesis gravidarum is hell. Dr Wei- Ni Lin Curry experienced hyperemesis gravidarum and was able to overcome it by using cannabis. She was lucky, since many women who experience HG end up undergoing unwanted abortions to save their lives. She published an excellent article called:”Hyperemesis Gravidarum and Clinical Cannabis: To Eat or Not to Eat”. In the article, she describes her own experience, as well as the experiences of other women suffering from HG. It should be required reading for all OB-GYNs.

Have Your Say


Related News