Meta-analysis: Cannabis Exposure Not Associated With Residual Adverse Impact On Cognitive Performance

Cannabis exposure in adolescents and young adults is not associated with any significant long-term detrimental effects on cognitive performance, according to a systematic literature review published today in the journal JAMA Psychiatry.

Investigators affiliated with the University of Pennsylvania, Perlman School of Medicine and with the Children’s Hospital of Pennsylvania reviewed data from 69 separate studies published between 1973 and 2017 involving 8,727 subjects (2,152 frequent or heavy users and 6,575 controls). Researchers reported no significant long-term deficits in memory, attention, or other aspects of cognitive functioning that could be independently attributed to cannabis use, regardless of subjects age of initiation. These findings are in contrast to similar studies assessing the impact of alcohol use and other controlled substances on cognition, which “have shown medium to large effect sizes.”

Authors concluded: “Associations between cannabis use and cognitive functioning in cross-sectional studies of adolescents and young adults are small and may be of questionable clinical importance for most individuals. Furthermore, abstinence of longer than 72 hours diminishes cognitive deficits associated with cannabis use. [R]esults indicate that previous studies of cannabis youth may have overstated the magnitude and persistence of cognitive deficits associated with marijuana use.”

Commenting on the study’s findings, NORML Deputy Director Paul Armentano said: “These conclusions are consistent with those of prior studies – in particular, recent longitudinal twin studies reporting that cannabis use is not independently associated with any residual change in intelligence quotient or executive function. These findings, combined with other recent studies reporting that cannabis exposure appears to have minimal adverse impact on brain morphology — particularly when compared to the dramatic effects of alcohol —dispute the long-standing ‘stoner-stupid’ stereotype, and should help to assuage fears that cannabis’ acute effects on behavior may persist long after drug ingestion.”

Presently, the medical use and dispensing of cannabis is regulated in 30 states. Eight states also regulate the retail sale of cannabis to adults. According to numerous peer-reviewed studies, neither the enactment of medicalization or adult use legalization has been linked to increased marijuana use or access by young people.

Full text of the new study, “Association of cannabis with cognitive functioning in adolescents and young adults: A systematic review and meta-analysis,” appears in JAMA Psychiatry.