Effects of prenatal marijuana exposure on neuropsychological outcomes in children aged 1-11 years: A systematic review

Background Normalisation of medicinal and recreational marijuana use has increased the importance of fully understanding effects of marijuana use on individual-and population-level health, including prenatal exposure effects on child development. We undertook a systematic review of the literature to examine the long-term effects of prenatal marijuana exposure on neuropsychological function in children aged 1-11 years. Methods Primary research publications were searched from Medline, Embase, PsychInfo, CINAHL EbscoHost, Cochrane Library, Global Health and ERIC (1980-2018). Eligible articles documented neuropsychological outcomes in children 1-11 years who had been prenatally exposed to marijuana. Studies of exposure to multiple prenatal drugs were included if results for marijuana exposure were reported separately from other substances. Data abstraction was independently performed by two reviewers using a standardised protocol. Results The eligible articles (n = 21) on data from seven independent longitudinal studies had high quality based on the Newcastle-Ottawa Scale. Some analyses found associations (P < 0.05) between prenatal marijuana exposure and decreased performance on memory, impulse control, problem-solving, quantitative reasoning, verbal development and visual analysis tests; as well as increased performance on attention and global motion perception tests. Limitations included concurrent use of other substances among study participants, potential under-reporting and publication biases, non-generalisable samples and limited published results preventing direct comparison of analyses. Conclusions The specific effects of prenatal marijuana exposure remain unclear and warrant further research. The larger number of neuropsychological domains that exhibit decreased versus increased psychological and behavioural functions suggests that exposure to marijuana may be harmful for brain development and function.