Marijuana use may affect cognition
March 13, 2006

PATRAS, Greece (United Press International) -- Greek researchers say they've determined memory, speed of thinking and other cognitive abilities become worse over time with heavy marijuana use.

The study found frequent marijuana users performed worse than non-users on tests of cognitive abilities, including divided attention and verbal fluency. Those who had used marijuana for 10 years or more had more problems with their thinking abilities than those who had used marijuana for five to 10 years. All of the marijuana users were heavy users, which was defined as smoking four or more joints per week.

"We found that the longer people used marijuana, the more deterioration they had in these cognitive abilities, especially in the ability to learn and remember new information," said study author Lambros Messinis of the Department of Neurology at the University Hospital of Patras in Patras, Greece. "In several areas, their abilities were significant enough to be considered impaired, with more impairment in the longer-term users than the shorter-term users."

The marijuana users performed worse in several cognitive domains, including delayed recall, recognition and executive functions of the brain.

The study's details appear in the March 14 issue of the journal Neurology.