European investigators looking to firm up whether or not there are residual effects of cannabis use on neurocognition say their findings suggest decision-making is not impaired when weed is used in moderation and when first use is after the age of 15.

Beyond that, researchers write in the study to be published this fall in Cognitive Development, “we find no evidence to support the presumption that cannabis consumption leads to a decline in neurocognitive ability.”

Investigators sought to get a fix on weed’s non-acute effects on neurocognition in adolescents. Specifically, they considered details on substance use and neurocognitive measures in 804 adolescents at age 14 and also at age 19.

Researchers did not detect any “significant neurocognitive differences before initiation of drug use,” the study notes. That said, after controlling for confounders, light cannabis use and late-onset of weed consumption “was associated with increased decision-making skills both cross-sectionally at follow-up, as well as longitudinally compared to non-using controls.”

Investigators say that the findings “highlight the importance of trajectories in cannabis use for neurocognition.”

A study in 2018 noted, “the purported neurocognitive effects of early cannabis onset may not be due to cannabis initiation alone, but also driven by limitations or late development of neurocognitive systems predictive of substance use.”

While a review published back in 2011 reported that “cannabis has a negative impact on cognition,” it did add “the current body of research literature does not provide evidence of significant, long-term effects due to cannabis use.”

Those findings seem to be in line with those of a review two years ago that suggests, whatever one’s age, regular, healthy cannabis users “display poorer neurocognitive functioning relative to non-users.”

Still, the authors emphasized, “more research (particularly large-scale longitudinal studies) is needed to identify critical periods or patterns of use that are more likely to result in negative outcomes.”