Rationale: Studies suggest that the adolescent brain is especially sensitive to cannabis, which can alter brain development leading to long-term behavioral changes.

Method: Researchers studied the effects of cannabis on brain development in adolescents by scanning the brains of 799 people between ages 13 and 16, and again 5 years later. They measured the size of the prefrontal cortex (PFC), an area of the frontal lobe that matures during adolescence. Along with the thickness of this part of the frontal lobe, they measured impulsive behavior because inhibiting impulses depends upon the PFC.

Results: Excess thinning of the PFC was observed in cannabis users. Those who hadn’t used at all during the 5-year period had the thickest PFC and were least impulsive. Using only 1-2 times was associated with slightly thinner cortices while using more than 40 times during adolescence led to the most shrinkage in the PFC.

Meaning: These data suggest that cannabis exposure during adolescence leads to excess thinning of the PFC, and more use leads to more shrinking, as well as increases in impulsivity.