Abstract
Cannabis use during pregnancy is increasing; the study of adverse outcomes in cannabis-exposed pregnancies is therefore important. Previous articles in this series described increased risks of maternal adverse outcomes, fetal adverse outcomes, birth defects in newborns, and autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) in childhood. This article examines neuropsychiatric adverse outcomes in offspring gestationally exposed to cannabis. Currently available research suggests that prenatal cannabis exposure is associated with increased risks of ASD, ADHD, psychosis proneness, psychotic like experiences, internalizing problems, externalizing problems, attention problems, thought-related problems, social problems, impaired executive function, and observed aggression. There is insufficient study of prenatal cannabis exposure and offspring IQ. Shortcomings in the existing literature are discussed; as examples, many outcomes were determined by screening rather than by formal assessment, prenatal cannabis exposure was ascertained retrospectively in some studies, childhood adverse experiences and exposures were seldom included as covariates, and details about cannabis use (source, potency, frequency, reasons) were unavailable. Curiously, the findings of adverse outcomes were inconsistent, and the effect sizes were small. Possible explanations are that women who use cannabis during pregnancy may not admit it and their pregnancy outcomes may then be misclassified into the control group, assessment of outcomes at too young an age or with insufficient accuracy may blur differences between exposed and unexposed groups, and adjustment for covariates may mask the full effects of cannabis. A last observation is that the studies reviewed were based on exposures that occurred decades ago. Given the increasing potency of currently available cannabis and the limitations of the existing research, it is possible that the available findings underestimate the breadth and severity of the risks. Cannabis is not a necessary substance for use during pregnancy, and so women who consider it safe might do well to guard against complacency and unnecessary exposure.