Continuous exposure to cannabis or marijuana is associated with worse verbal memory, revealed a new study.
The study published in the Journal JAMA Internal Medicine was conducted by a team of researchers from the University of California at San Francisco and the University of Lausanne in Switzerland.
They examined adults between ages 18 and 30, who were enrolled in the Coronary Artery Risk Development in Young Adults (CARDIA) study in 1985 and 1986. Among the 3,385 participants, 84% reported past cannabis use but only 11% continued to use the drug into middle age.
The tests covered verbal memory, measured by the ability to memorize and recall a list of 15 words; visual motor speed; working memory; sustained attention skills; and the ability to problem-solve and plan.
Researchers found that the for every five years of smoking, there was a slight reduction in word recall-the equivalent of one out of two past smokers remembering one fewer words than non-smokers on a list of 15 memorized words. But there was no impact on the processing speed.
The team also found that the higher an individual's lifelong exposure to pot, the more their verbal memory seemed to have dimmed by middle age.