Challenging the 25-year-old ‘mature brain’ mythology: implications for the minimum legal age for non-medical cannabis use

The minimum legal age (MLA) for non-medical cannabis use remains a contentious issue. While current regulations range from 18 to 21 years across jurisdictions, some advocates propose raising the threshold to 25, arguing that brain maturation continues until that age. They postulate that even individuals 22 through 25 exhibit increased neurodevelopmental vulnerability to cannabis. This Perspective examines this assertion, discussing the neuroscientific evidence on brain development and its implications for setting legal age limits for cannabis use. While most major macrostructural and microstructural brain development occurs early in life, processes such as synaptic pruning, gene expression, and prefrontal cortical changes persist through adolescence, with more subtle changes extending into the third decade. Nonetheless, there is no empirically defined neurodevelopmental endpoint at age 25. Brain maturation is a nonlinear process, region-specific, influenced by sex and specific physiological processes. Importantly, existing evidence does not demonstrate greater long-term cognitive or neurophysiological harm attributable to cannabis use in individuals aged 18-25 years compared to those older than 25. This Perspective concludes that an MLA between 18-21 years is a scientifically supportable and socially coherent threshold for non-medical cannabis use. Policy decisions should be informed not only by neurobiological evidence but also by legal, justice, sociocultural, psychological, and historical considerations.