In adults, studies examining the long-lasting cognitive effects of
marijuana use demonstrate subtle deficits in attention, executive
function, and memory. Because neuromaturation continues through
adolescence, these results cannot necessarily generalize to adolescent
marijuana users. The goal of this study was to examine neuropsychological
functioning in abstinent marijuana using and demographically similar
control adolescents. Data were collected from 65 adolescent marijuana
users (n = 31, 26% females) and controls (n = 34, 26%
females) 16–18 years of age. Extensive exclusionary criteria
included independent psychiatric, medical, and neurologic disorders.
Neuropsychological assessments were conducted after > 23 days of
monitored abstinence. After controlling for lifetime alcohol use and
depressive symptoms, adolescent marijuana users demonstrated slower
psychomotor speed (p < .05), and poorer complex attention
(p < .04), story memory (p < .04), and planning
and sequencing ability (p < .001) compared with controls.
Post hoc analysis revealed that the number of lifetime marijuana
use episodes was associated with poorer cognitive function, even after
controlling for lifetime alcohol use. The general pattern of results
suggested that, even after a month of monitored abstinence, adolescent
marijuana users demonstrate subtle neuropsychological deficits compared
with nonusers. It is possible that frequent marijuana use during
adolescence may negatively influence neuromaturation and cognitive
development. (JINS, 2007, 13, 807–820.)