Marijuana use could pose serious cognitive function risk later in life

Marijuana is the most frequently used illicit drug in the United States, according to a recent survey from the National Survey on Drug Use and Health, and new data suggest that marijuana use now could pose a serious cognitive function risk later in life.

Stefan Kertesz, M.D., an associate professor with the University of Alabama at Birmingham School of Medicine, is part of a recently published nationwide study reporting potential long-term consequences with implications for public health.

Impaired cognitive functioning is an acute effect of marijuana use, and there is increasing evidence that such effects may persist later in life after marijuana use has ceased. Heavy, long-term use of marijuana has been associated with cognitive impairment, particularly in learning and remembering new information.

Kertesz and other researchers found past exposure to marijuana use to be significantly associated with worse verbal memory in middle age.

Their paper used data from the Coronary Artery Risk Development in Young Adults (CARDIA) study which started in 1985, where more than 5,000 healthy adults were regularly asked about marijuana use. In contrast to studies that focus on people known to have an addiction, this study focused on community-based adults, where casual use tends to be more common than addiction.

In the final year of the study, CARDIA participants underwent simple cognitive tests, including a word memory test. Individuals were presented with 15 words and then asked to try to remember them. After 25 minutes, they were later asked to recall the words. The tests showed that there was a significant decline in verbal memory among persons whose cumulative marijuana use exceeded the equivalent of one joint a day for five years.

"For every five years of marijuana exposure, one out of two participants would remember one word less," Kertesz said.

Kertesz also said that it is important to realize that marijuana is more potent today than it was in the 1980s, raising the possibility that users of today's marijuana may face cognitive consequences of greater magnitude than those reported.

"It's crucial to recognize that young brains are truly different and not fully developed until age 22 and are at more risk from marijuana," he said. "Parents and teachers need to be vigilant that this poses a larger risk to adolescents."

Data from 2012 indicates that, among students in the 12th grade (ages 17-18 years), 37 percent had used marijuana within the last year, 23 percent within the last 30 days and 6.5 percent daily.