Numerous studies published between 1999 and 2001 challenge a report published today in JAMA (The Journal of the American Medical Association) that marijuana smoking negatively impacts cognitive function.
“The only significant long-term impact marijuana has upon cognitive function is upon those who continue to irrationally demonize and criminalize this plant,” said Allen St. Pierre, Executive Director of The NORML Foundation.
The JAMA study measured the cognitive skills of long-term marijuana users seeking treatment for perceived cannabis dependence, many of whom voiced previous concerns about perceived cognitive impairments. Controls (short-term and non-users of marijuana) were selected from the general population. Researchers found that long-term users who had abstained from marijuana for an average of 17-hours performed significantly worse than controls on tests of memory and attention.
However, previous studies of long-term marijuana smokers not in treatment have reached the opposite conclusion.
In October, researchers at Harvard University reported that regular marijuana smokers who abstain from pot for one week or more performed no differently on cognitive tests than non-smokers. According to findings published in The Archives of General Psychiatry, chronic daily smokers “showed virtually no significant differences from control subjects (those who had smoked marijuana less than 50 times in their lives) on a battery of 10 neuropsychological tests.” The researchers concluded that their findings “do not support the hypothesis that long-term heavy cannabis use causes irreversible cognitive deficits.”
A recent meta-analysis of neuropsychological studies of long-term marijuana smokers presented this summer at the NIDA (National Institute on Drug Abuse) Workshop on the Clinical Consequences of Marijuana also found no deficits in 7 of 8 neuropsychological ability areas. “The studies … yielded no basis for concluding that long-term cannabis use is associated with generalized neurocognitive decline,” the researchers concluded.
Additionally, a 1999 study of 1,300 volunteers published in The American Journal of Epidemiology found that marijuana smoking, even long-term, failed to significantly impact cognition. Researchers administered subjects Mini-Mental State Examinations (MMSE) in 1981 and 1982, and then measured their performance on follow up tests some 12 to 15 years later. In all, researchers found “no significant differences in cognitive decline between heavy users, light users, and nonusers of cannabis.”
Large government-sponsored studies conducted during the 1970s in Jamaica, Greece and Costa Rica on marijuana smoking and cognition also reported no significant differences between long-term smokers and non-smokers.
NORML Foundation Chair and City University of New York (CUNY) medical professor John P. Morgan M.D. said, “Based on this evidence, it does not appear that long-term marijuana use causes any significant permanent harm to intellectual ability.”
For more information, please contact either Allen St. Pierre or Paul Armentano of The NORML Foundation at (202) 483-8751.