Effects of regular cannabis use on neurocognition, brain structure, and function: a systematic review of findings in adults

Background: Cannabis is the most used illicit drug worldwide. The long-standing consequences for the central nervous system associated with frequent cannabis use have not been well delineated and should be determined. Objective: To review recent studies on the effects of regular cannabis use regarding its effects on cognition, brain structure, and function in adults. Methods: A systematic literature review was conducted by performing electronic searches in the PubMed, LILACS, and SciELO databases (2010-2016). The initial search identified 898 records. They were evaluated for relevance according to the inclusion and exclusion criteria and 56 studies were included. Results: The neuropsychological studies provide evidence for subtle cognitive deficits at least 7 days after heavy cannabis use. The structural neuroimaging studies show growing evidence of abnormalities in hippocampus volume and gray matter density of cannabis users relative to controls; however, morphological changes in other brain regions are more controversial. The functional neuroimaging studies suggest an altered pattern of brain activity associated with cannabis use. Conclusion: Although there are several limitations for study comparison and substantial heterogeneity in the findings, the present review suggests that regular cannabis use is associated with mild cognitive changes in addition to structural and functional alterations in the brain in adults. The morphological alterations could ultimately affect brain organization and function, but the associated time course for neuronal recovery as well as the real impact on cognitive functioning remain unknown. Also, it is still unclear whether the identified alterations are as a consequence of or precede cannabis use.