Past Pot Use Has No Negative Impact On Intelligence, Canadian IQ Study Says

Ottawa, Ontario:  Marijuana smoking, even long-term, does not harm intelligence, according to findings published this week in the Canadian Medical Association Journal. 

Researchers report that former pot smokers who had, on average, consumed an estimated 5,793 marijuana cigarettes over 38 months experienced no negative measurable effects on intelligence quotient (IQ).  Researchers did note a minor decrease in IQ among current heavy users (those who smoke more than five joints per week), but noted that their scores still remained above average for their age group.

Authors called pot’s minimal negative impact on IQ striking.  “We conclude that marijuana does not have a long-term negative impact on global intelligence,” they wrote.

Previous assessments of marijuana use on cognition have reported similar results.  Most recently, a study published in The Archives of General Psychiatry found that marijuana smokers who abstained from pot for at least a week performed no differently on cognitive tests than non-smokers.  In addition, a 1999 study of 1,300 volunteers published in The American Journal of Epidemiology reported “no significant differences in cognitive decline between heavy users, light users, and nonusers of cannabis” over a 15-year period.

For more information, please contact either Allen St. Pierre or Paul Armentano of The NORML Foundation at (202) 483-8751.  The CMAJ study is available online at: