Parents and their children often face separation and other punishments due to the idea that prenatal cannabis exposure causes brain damage in children. A new review of cannabis literature, however, has found that exposure to the substance in the womb does not lead to affect the unborn children's brain development.
For the review, researchers from Columbia University, the New York State Psychiatric Institute, and Swinburne University analyzed 1604 articles discussing the topic, of which 45 were selected for full-text review after the exclusion of irrelevant studies.
The selected studies ranged in sample size from 9 (for cannabis-exposed children) to 538 (for children in control groups). The length of the follow-ups ranged from 2 months to 22 years. In total, the researchers were able to make 1,001 statistical comparisons among the studies.
The researchers found that, generally speaking, prenatal exposure to cannabis was associated with few effects- both negative and positive. From all the studies taken together, less than 5% showed any statistical difference between children's cognitive test scores. Among those that displayed differences, just 0.3% fell out of the normal range.
"Overall, we found a total of 1,001 statistical comparisons between groups of participants that were exposed to cannabis prenatally and non-exposed controls ... [and] despite analyzing studies spanning approximately three decades, we conclude the evidence does not support an association between prenatal cannabis exposure and clinically relevant cognitive deficits," write the researchers.
"The clinical implications of these subtle differences [are also] nearly impossible to determine without knowledge of the expected range of performance for a particular group [through] the use of normative data ... a core assessment principle in clinical neuropsychology [that] appears to be largely ignored in the literature on prenatal cannabis exposure," they continue.
Given that there are many legal and medical policies based on prenatal cannabis exposure, the authors of the review hope that their findings will inform public policy and lawmakers to reconsider past rulings.