From NORML-USA

 

Cognitive Performance Unaffected After Marijuana Smoking - Pot "Has No Effect on Accuracy," Study Reveals

   New York, NY: Marijuana smoking has virtually no effect on complex cognitive task performance - including reaction time, memory and mental calculation - in experienced users, according to the findings of a Columbia University study published in this month's issue of Neuropsychopharmacology. 

    "Although marijuana significantly increased the number of premature responses and the time participants required to complete several tasks, it had no effect on accuracy on measures of cognitive flexibility, mental calculation, and reasoning," researchers concluded.  "The relatively few accuracy impairments observed is congruent with several other studies investigating acute marijuana effects on psychomotor and simple cognitive performance.  Moreover, the present data expands these findings by showing that more complex cognitive performance is only minimally affected following acute marijuana smoking."

    Eighteen subjects participated in the three-session outpatient study.  During each session, participants completed a battery of baseline computerized cognitive tasks in various domains, including reaction time, attention, memory, visuospatial processing, reasoning, flexibility and mental calculation.  Subjects were then administered marijuana cigarettes ranging from zero to 3.9 percent THC in a double-blind fashion before completing another series of cognitive tests 20 minutes later.

    Researchers found subjects' accuracy on the tests was unaltered following their use of marijuana.  "In summary,
... the finding that accuracy was unaffected by smoked marijuana indicates that heavy, daily marijuana smokers will not fulfill the DSM-IV [Diagnostic and Statistical Manual of Mental Disorders, 4th edition] criterion for marijuana intoxication that requires impairment of complex
cognitive functioning," authors concluded.

    The study's findings follow those of a Harvard study published last month in the Archives of General Psychiatry determining that long-term marijuana smokers who abstain from the drug for one week or more perform identically on cognition tests as nonusers.  A previous study on marijuana and cognition by researchers at John Hopkins University in Baltimore found "no significant differences in cognitive decline between heavy users, light users, and nonusers of cannabis" over a 15-year period in a cohort of 1,318 subjects.