SAN FRANCISCO (CBS SF) — A new study conducted by researchers at the University of California at San Francisco found that lifetime marijuana users had worse verbal memory in middle age, but found no deficiencies in other measures of cognitive function.

Published in the Journal of the American Medical Association- Internal Medicine on Feb. 1, the study does not tease out cause and effect, meaning that lower verbal memory could be either a cause or a consequence of marijuana use, noted the study’s lead author Reto Auer, MD, MAS.

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The study was the result of researchers tracking 3,000 middle-aged adults over 25 years.

Of the 3,000 adults tracked, those who used marijuana for more than five years cumulatively had worse verbal memory in middle age than their peers who smoked marijuana less often.

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The study maintains that marijuana use is associated with worse verbal memory, but does not appear to affect other domains of cognitive function as other studies have suggested.

Marijuana use was not found to be associated with the cognitive functions of processing speed and executive functioning, which controls information organization and focus, according to the study.

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For heavier, long-term marijuana users, defined as daily use for 10 or 20 years, other studies have found drops in IQ, as well as poor verbal learning, memory and attention.