A review of the research on the negative health affects of marijuana published today in the New England Journal of Medicine reports that smoking pot as a kid may have lasting impacts on intelligence and achievement.

For starters, smoking pot regularly from an early age is correlated with a lower IQ. The mechanism is not fully understood—experts are not claiming one necessarily causes the other—but scientists speculate the drug can interfere with a critical period for brain development during the teen years. “Adults who smoked regularly during adolescence” according to the review, have “impaired neural connectivity” in parts of the brain involving alertness and self conscious awareness, executive function, processing of habits and routines, learning, and memory.