In the current issue of debate about marijuana laws and interest in marijuana as medicine one issue remains unresolved: Does heavy, frequent, or prolonged use of cannabis lead to a deterioration in cognitive function that persists well beyond any period of acute intoxication? Is the functioning of the brain altered in the long term? With over 7 million people using cannabis weekly and the potential for increased physician recommendations for select patients to use cannabis therapeutically, answers to these questions are of significant public concern. Scientific evidence from past research clearly showed that gross impairment related to chronic cannabis use did not occur but was inconclusive with regard to the presence of more specific deficits. Recent studies with improved methods however have demonstrated changes in cognition and brain function associated with long-term or frequent use of cannabis. Specific impairments of attention, memory, and executive function have been found in cannabis users in the unintoxicated state in controlled studies using brain event-related potential techniques and neuropsychological assessments including complex tasks.
Brain imaging studies of cannabis users have demonstrated altered function, blood flow, and metabolism in prefrontal and cerebella regions.
This study investigated the nature of cognitive impairments associated with long-term cannabis use employing data collected from a large clinical trial of chronic users seeding treatment for cannabis dependence. The study compared 102 cannabis users assessed prior to treatment on carefully selected neuropsychological tests with 33 nonuser controls. The effects of cannabis use that contribute to impairment were examined. Nine tests were administered which included 2 tests which evaluated the persons IQ after the 3 year study.
In the study they compared the long term users with an average of 24 years of regular use with the shorter term users with a mean of 10 years of regular use and the nonusers...