As cannabis legalization expands across multiple continents, understanding its cognitive costs — particularly for developing brains — has become a pressing public health question. This systematic review adds a layer of geographic nuance largely absent from prior analyses, suggesting that where and when someone uses cannabis may shape the magnitude of harm as much as the drug itself.
Drawing on 22 studies published between 2019 and 2024 and identified through a PRISMA-compliant search across four major databases, the review found that episodic and working memory impairments were the most consistently observed deficits among adolescent and young adult cannabis users. Executive function outcomes, by contrast, proved heterogeneous — varying with age group, frequency and duration of use, study design, and the specific cognitive tasks employed. A notable geographic split emerged: studies from the Americas — many of them longitudinal in design — more frequently documented negative associations between cannabis use and cognitive performance, while European findings were more mixed, a pattern the authors tentatively attribute to differences in cannabis product composition.
The geographic divergence is arguably the most analytically interesting signal in this dataset, though it warrants considerable caution. Variation in THC-to-CBD ratios across regional cannabis markets, differences in age of first use, socioeconomic confounders, and disparate study methodologies could all generate apparent continental differences without reflecting any true biological distinction. The memory findings, however, align with a robust body of neuroimaging and longitudinal work linking adolescent cannabis exposure to hippocampal volume changes and disrupted prefrontal-hippocampal connectivity — mechanisms plausible in both developmental and adult brains. With only 22 eligible studies and significant heterogeneity, this review is best read as a mapping exercise rather than a definitive causal account. Its primary value lies in flagging that region-specific product characteristics — particularly THC concentration — may be an underappreciated variable in cognitive risk models, an insight that should inform both future study design and the conversation around potency regulation.