Memory, attention, and verbal fluency appear to suffer among regular, long-term marijuana users, HealthDay News reported March 14.

A team of researchers from University Hospital in Patras, Greece found that people who smoked four joints or more per week tended to perform poorly on mental tests, and those who had smoked regularly for a decade or more did the worst. "The longer you smoke marijuana, the more likely you are to experience a diminution of cognitive functions that are critical for 'normal' daily functioning," said Barbara Flannery, an addiction researcher.

Researchers found, for example, that long-term marijuana users were impaired 70 percent of the time on a decision-making test, compared to 55 percent for short-term users and 8 percent for nonusers.

Researchers cautioned, however, that the purported link between marijuana and diminished mental acuity is far from definitive.

The study was published in the March 14 issue of the journal Neurology.