06 January 08 - 20:49
Cannabis, cognition & memory
What about claims of cannabis' damaging effect of cognition?
A review of the scientific literature indicates that rumors regarding the " stupid stoner" stereotype are unfounded. According to clinical trial data published this past spring in the American Journal of Addictions, cannabis use -- including heavy, long-term use of the drug -- has, at most, only a negligible impact on cognition and memory.
Researchers at Harvard Medical School performed magnetic resonance imaging on the brains of 22 long-term cannabis users (reporting a mean of 20,100 lifetime episodes of smoking) and 26 controls (subjects with no history of cannabis use). Imaging displayed "no significant differences" between heavy cannabis smokers compared to controls, the study found.
Previous trials tell a similar tale. An October 2004 study published in the journal Psychological Medicine examining the potential long-term residual effects of cannabis on cognition in monozygotic male twins reported "an absence of marked long-term residual effects of cannabis use on cognitive abilities."
A 2003 meta-analysis published in the Journal of the International Neuropsychological Society also "failed to reveal a substantial, systematic effect of long-term, regular cannabis consumption on the neurocognitive functioning of users who were not acutely intoxicated," and a 2002 clinical trial published in the Canadian Medical Association Journal determined, "Cannabis does not have a long-term negative impact on global intelligence."
Finally, a 2001 study published in the journal Archives of General Psychiatry found that long-term cannabis smokers who abstained from the drug for one week "showed virtually no significant differences from control subjects (those who had smoked cannabis less than 50 times in their lives) on a battery of 10 neuropsychological tests." Investigators further added, "Former heavy users, who had consumed little or no cannabis in the three months before testing, [also] showed no significant differences from control subjects on any of these tests on any of the testing days."
(References:
Lack of hippocampal volume change in long-term heavy cannabis users. American Journal of Addictions. 2005 | Neuropsychological consequences of regular marijuana use: a twin study. Psychological Medicine. 2004 | Non-acute (residual) neurocognitive effects of cannabis use: A meta-analytic study. Journal of the International Neuropsychological Society. 2003 | Current and former marijuana use: preliminary findings of a longitudinal study of effects on IQ in young adults. Canadian Medical Association Journal. 2002 | Neuropsychological Performance in Long-term Cannabis Users. Archives of General Psychiatry. 2001)http://www.norml.org/index.cfm?Group_ID=6812#Neurogenesis
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