BOSTON – People taking prescription antidepressants appear to drive worse than people who aren't taking such drugs, and depressed people on antidepressants have even more trouble concentrating and reacting behind the wheel.

These were the conclusions of a study released Sunday at the Annual Convention of the American Psychological Association.

University of North Dakota psychologists Holly Dannewitz. PhD, and Tom Petros, PhD, recruited 60 people to participate in a driving simulation in which participants had to make a series of common driving decisions, such as reacting to brake lights, stop signs or traffic signals while being distracted by speed limit signs, pylons, animals, other cars, helicopters or bicyclists. The simulation tested steering, concentration and scanning. Thirty-one of the participants were taking at least one type of antidepressant while 29 control group members were taking no medications with the exception of oral contraceptives in some cases.

The group taking antidepressants was further divided into those who scored higher and lower on a test of depression. The group taking antidepressants who reported a high number of symptoms of depression performed significantly worse than the control group on several of the driving performance tasks. But participants who were taking antidepressants and scored in the normal range on a test to measure depression performed no differently than the non-medicated individuals.

"Individuals taking antidepressants should be aware of the possible cognitive effects as [they] may affect performance in social, academic and work settings, as well as driving abilities," the researchers wrote. "However, it appears that mood is correlated with cognitive performance, more so than medication use."

This research is important in light of the rapid increase in the number of Americans taking antidepressants. Americans' use of antidepressant drugs such as Prozac, Paxil or Zoloft, nearly tripled in a decade, according to the 2004 Health United States report, issued by the National Center for Health Statistics. Among women, one in 10 takes an antidepressant drug, according to the government.

Source: American Psychological Association