A critical examination of the "brain matures at 25" claim finds no empirically defined neurodevelopmental endpoint at that age and no evidence that cannabis causes greater long-term harm in 18-25-year-olds compared to older adults.
Cannabis policymakers setting legal age thresholds; neuroscientists communicating brain development research.
No empirically defined neurodevelopmental endpoint exists at age 25
What the researchers found
While brain development continues into the third decade, there is no empirically defined endpoint at age 25. Brain maturation is nonlinear, region-specific, and influenced by sex. Existing evidence does not demonstrate greater long-term cognitive or neurophysiological harm from cannabis in individuals aged 18-25 compared to those over 25. An MLA of 18-21 is scientifically supportable.
Why it matters
The "brain doesn't mature until 25" claim has become a popular argument for raising cannabis legal ages, but this review finds it oversimplifies neurodevelopmental science. Policy decisions based on a mythologized age threshold may create more harm (through criminalization of young adults) than they prevent.
The numbers in context
Current legal age limits range from 18-21 across jurisdictions. Some advocates propose age 25. Major brain structural development occurs early in life. Synaptic pruning and prefrontal changes continue through adolescence with subtle changes into the 20s.
How the study worked
Perspective/commentary examining neuroscientific evidence on brain development and its implications for setting legal cannabis age limits. Reviews macrostructural and microstructural brain development, synaptic pruning, gene expression, and prefrontal cortical changes.
What this study cannot tell us
This is a perspective piece, not a systematic review. The authors argue a specific policy position, which inherently involves value judgments beyond pure science. Brain development research is ongoing and new findings could shift the evidence.
How to read the evidence
Moderate: well-argued perspective grounded in neuroscience literature, but a commentary rather than a systematic evidence synthesis.
When this study was published
2025 perspective.
The bigger picture
Setting legal thresholds requires balancing neuroscience with legal, social, and justice considerations. A policy that criminalizes 22-year-olds for cannabis use based on a misrepresented neuroscience claim could cause more harm to young adults than the cannabis exposure it aims to prevent.
Questions still open
- Would an age-graduated system (e.g., lower THC potency limits for 18-21) be a better approach than a hard cutoff? How do justice system harms from criminalization of young adult cannabis use compare to potential neurological harms?
Common questions
Does the brain stop developing at 25?
Is cannabis safer after age 25?
Read the original research
Challenging the 25-year-old 'mature brain' mythology: implications for the minimum legal age for non-medical cannabis use.
The American journal of drug and alcohol abuse, 51(5), 577-583
Citation
Adinoff, Bryon; Nunes, Julio C. (2025). Challenging the 25-year-old 'mature brain' mythology: implications for the minimum legal age for non-medical cannabis use.. The American journal of drug and alcohol abuse, 51(5), 577-583. https://doi.org/10.1080/00952990.2025.2561982