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Study Finds No Long Term Cognitive Impairment From Marijuana Use

Posted by Jason Draizin on 07/22/2011 in Medical Marijuana Research

A new study published in the journal Addiction shows that contrary to popular belief, even among many advocates, marijuana does not appear to cause any long-term cognitive impairment. The research followed almost 2,000 Australian adults aged 20 to 24for eight years as part of a project on community health.The study sample included current heavy users, mild users, former users and non-smokers.


Researchers administered memory and intelligence tests three times over the eight years and kept track of how each participant's smoking behavior changed over time. After taking gender and education out of the equation (because men and those with lower education levels were more likely to smoke marijuana, they initially skewed the results.) they discovered that differences in performance between users and non-users disappeared almost entirely.


A test that required immediate recall of nouns was the one stand-out in which heavy users underperformed. However, further testing revealed that after they stopped smoking the performance difference disappeared. Ultimately the study, lead by Robert Tait from the Australian National University , concluded that:


"Cessation of cannabis use appears to be associated with an improvement in capacity for recall of information that has just been learned. No other measures of cognitive performance were related to cannabis after controlling for confounds."


Interestingly, last year another study found that many marijuana users unconsciously submitted to the stereotype and actually performed differently on cognitive tests when researchers included the "stoner" image into their prompts. While men performed worse if reminded of the stereotype and women did better, the data clearly showed that the effects of marijuana itself were negligence.