Teen Marijuana Use Linked With Lower Adult IQ Scores

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A recent report coming out of New Zealand suggests that individuals that were heavy marijuana users as adolescents had “consistently lower IQs” as adults than subjects that had either never used marijuana as teens or didn’t begin using the drug until later on in their adulthood.

According to the report, Persistent Cannabis Users Show Neuropsychological Decline from Childhood to Midlife, which was published in the Proceedings of the National Academy of Sciences, individuals that began using marijuana at least four times a week as adolescents fostered IQs at 38 that were eight points lower than a majority of the population studied.

The longitudinal study evaluated more than 1,000 subjects over a 25-year span, beginning with neurological testing of the population at age 13.

According to the researchers, persistent marijuana use was closely associated with “neuropsychological decline broadly across the domains of functioning, even after controlling for years of education.” The study said that heavy marijuana users reported more cognitive problems, with adolescent-onset users reporting greater levels of neuropsychological impairment than the other subjects.

Researchers said that cessation of marijuana use later in adulthood did not fully restore the neuropsychological functioning capabilities of adolescent-onset marijuana users, ultimately suggesting the possibility of a neurotoxin effect for youth that began using marijuana before turning 18.