In a 25-year study, researchers from Switzerland found that middle-aged people who smoked marijuana or weed during their teenage and young adult years have poorer verbal memory. Findings showed that life-long use of marijuana was associated with poor performance in the three areas of cognitive function.
In a randomized study, the researchers enrolled over 5,000 young adults aged 18 and 30 years old and followed them for 25 years in various points in their lives. After 25 years, over 3,400 were left in the study. About 84.3 percent said they used marijuana in the past while 11.6 percent said they continued using marijuana into middle age.
The team measured the participants' cognitive function with tests that focused on speed processing, verbal memory and executive function. Participants who continued smoking marijuana up to the point of tests had poorer speed processing and verbal memory. They found that life-long exposure to the cannabis was linked to poor performance in the three areas tested. Verbal memory decreased by 0.13 standardized units for every five years of past marijuana exposure.
"In this study, there are as much women as men, as much black as white, as much lower education as higher education. It provides a better sense of what the association is in the overall population," said study author Dr. Reto Auer from Switzerland's University of Lausanne.
Past marijuana exposure didn't seem to disturb other areas of cognitive function apart from verbal memory. However, the researchers weren't able to conclude if occasional use of marijuana during adolescence carries long-term memory effects. It is also unclear if this occasional usage affects other aspects of cognitive function. The study was published in the journal JAMA Internal Medicine.
Reto said that the participants who occasionally used marijuana smoked to get high and take advantage of the resulting 'transient change.' However, it could be carrying toxic effects that can directly disturb the neurons. It could also have long-term effects on the brain's way of processing information.
"These findings fit well with other evidence on the effects of long-term marijuana use on cognitive performance," wrote Wayne Hall, Ph.D. and Michael Lynskey, Ph.D. on a commentary article published in the JAMA Internal Medicine on Feb. 1
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