Specific attentional dysfunction in adults following early start of cannabis use

Rationale and objective: The present study tested the hypothesis that chron ic interference by cannabis with endogenous cannabinoid systems during peri pubertal development causes specific and persistent brain alterations in hu mans. As an index of cannabinoid action, visual scanning, along with other attentional functions, was chosen. Visual scanning undergoes a major matura tion process around age 12-15 years and, in addition, the visual system is known to react specifically and sensitively to cannabinoids. Methods: From 250 individuals consuming cannabis regularly, 99 healthy pure cannabis user s were selected. They were free of any other past or present drug abuse, or history of neuropsychiatric disease. After an interview, physical examinat ion, analysis of routine laboratory parameters, plasma/urine analyses for d rugs, and MMPI testing, users and respective controls were subjected to a c omputer-assisted attention test battery comprising visual scanning, alertne ss, divided attention, flexibility, and working memory. Results: Of the pot ential predictors of test performance within the user group, including pres ent age, age of onset of cannabis use, degree of acute intoxication (THC+TH COH plasma levels), and cumulative toxicity (estimated total life dose), an early age of onset turned out to be the only predictor, predicting impaire d reaction times exclusively in visual scanning. Early-onset users (onset b efore age 16; n = 48) showed a significant impairment in reaction times in this function, whereas late-onset users (onset after age 16; n = 51) did no t differ from controls (n = 49). Conclusions: These data suggest that begin ning cannabis use during early adolescence may lead to enduring effects on specific attentional functions in adulthood. Apparently, vulnerable periods during brain development exist that are subject to persistent alterations by interfering exogenous cannabinoids.