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Invited Commentary
March 2016

Long-term Marijuana Use and Cognitive Impairment in Middle Age

Author Affiliations
  • 1Centre for Youth Substance Abuse Research, The University of Queensland, Queensland, Australia
  • 2National Addiction Centre, Kings College London, United Kingdom
JAMA Intern Med. 2016;176(3):362-363. doi:10.1001/jamainternmed.2015.7850

During the last 20 years, there have been substantial changes in the legal status and public perception of marijuana in the United States. Decriminalization, medical dispensaries with marijuana for those with a physician’s note, and legalization of marijuana in several states have resulted in increased availability and more relaxed views toward marijuana use. However, to our knowledge, relatively little research has been done on the risks of long-term marijuana use.

In this issue of JAMA Internal Medicine, Auer and colleagues1 report an association between cumulative lifetime marijuana exposure and cognitive performance in a prospective study of 3385 middle-aged adults who were followed up for 25 years. Their findings suggest that those who used marijuana on a long-term daily basis have poorer verbal memory in middle age than do their peers who have not smoked marijuana habitually.

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    1 Comment for this article
    Verbal deficits: cause or effect of cannabis abuse?
    David L. Keller, MD | none
    Multiple studies have now demonstrated an association between neurological degeneration and chronic cannabis use during adolescence and young adulthood. Given that mature brains share mechanisms of repair and learning with young brains, to the extent that these abilities are retained, there is little to suggest that the effects of cannabis will be found to be any kinder to mature brains. Still, legalization of cannabis can be justified by the following arguments:
    1) Legalization will dissipate the counter-cultural allure of the officially banned weed.
    2) Legalization will neutralize arguments that corporate puppet-masters (or whomever) are conspiring to repress the users of
    this weed
    3) There are worse things than verbal deficits. I can't think of any off-hand, but I don't want to impose my values on the less communicative.
    4) While cannabis is clearly harmful, its harms occur slowly and over sufficient time for the abuser to give it up before the damage is too far gone (usually).
    5) Full legalization will remove these debates from pages better devoted to the advancement of medical science.