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Does prenatal exposure to cannabis cause cognitive impairment?

Researchers from Columbia University have just confirmed what many people already knew – that public policy regarding cannabis tends to be based on scientific findings that are murky at best and non-existent at worse. In a new study, the team probed the widely  accepted idea that cannabis use during pregnancy hinders infants’ cognitive development, and found that there has never been any real evidence to support this. 

It’s worth noting that this doesn’t mean that smoking weed while pregnant is definitely safe, but rather that there is no categorical proof that prenatal exposure to cannabis causes mental impairment. This is pretty significant when you consider that some 1,600 studies on the impact of marijuana on fetal cognition have been conducted over the past three decades.  

With that in mind – and at a time when dispensaries are increasingly offering cannabis products as treatments for morning sickness – the tendency of policymakers to cling to such unproven notions about the risks and benefits of these medications is only creating unnecessary confusion and suffering. So the question is, how has this erroneous idea been allowed to persist for so long? 

In an attempt to solve this conundrum, the authors reviewed every study that has ever looked into the impact of prenatal cannabis exposure on cognition later in life. Before starting, they discarded all studies involving rats, and were left with a stack of research papers that described actual people who had been exposed to cannabis while in the womb. 

The combined literature contained only three instances in which the cognitive test results of these people fell below the normal range, out of a total of 1,004 comparisons. In other words, “cognitive performance scores of cannabis-exposed groups overwhelmingly fell within the normal range when compared against normative data.” 

The problem, however, is that many studies didn’t compare the cognitive performance of these people with universal averages, but instead pitted people who had been prenatally exposed to cannabis with those who hadn’t. Unfortunately, this approach fails to consider all the other factors that may contribute to differing scores between the two groups, such as the maternal cognitive ability, home environment and education. 

To highlight this, the researchers single out a study in which young children whose mothers had smoked weed while pregnant performed worse than those whose mothers did not. However, it later turned out that the kids who had been prenatally exposed to cannabis had generally had less access to preschool than their non-exposed counterparts. When the researchers then matched up the children up based on the amount of time they had spent in preschool, they found that prenatal weed exposure had no impact on cognitive performance. 

In another study, most of the mothers who used cannabis while pregnant had also used tobacco, and statistical analysis revealed that it was the tobacco rather than marijuana that was responsible for any of their children’s mental shortcomings. 

Long story short, the study authors are essentially trying to point out that many common beliefs about cannabis are based on unreliable studies that don’t take into account the multitude of lifestyle factors that influence things like cognitive capacity. Once you level the field and correct for all of these factors, then it seems impossible to find any evidence that prenatal exposure to marijuana causes cognitive impairment later in life. 

Of course, this study doesn’t look into any of the other purported risks associated with using cannabis during pregnancy, such as reduced birthweight. It is not, therefore, a green light to hit the bong without restraint if you are expecting, although it should at least come as a relief to anyone with stoner parents. 

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

Ben Taub