Updated: December 17, 2018

SUNDAY, August 17, 2008 ( — Are antidepressant users worse drivers than those who don't take the drugs? A new study suggests this could be the case, although it’s not entirely clear if it’s the use of the medication or the underlying depression that's to blame.

In the study, psychologist Holly Dannewitz, PhD, and a colleague recruited 60 people who were mostly in their 20s to take a simulated driving test. Half of the subjects were taking an antidepressant and the other half were on no medications at all, aside from oral contraceptives.

The test wasn’t a Sunday drive. The subjects had to steer smoothly around a track; follow a car in front of them; hit a “brake pedal” when they saw taillights; and click a paddle or hit a button when they saw a red light, traffic hazard, or stop sign.

Overall, antidepressant users performed worse on the test than those not taking the drugs, according to the study, which will be presented at the American Psychological Association meeting in Boston this weekend. But it wasn't clear if it was depression or the medication used to treat depression that may have affected their driving skills.

So the researchers measured the mood of the antidepressant users, and then divided them into two groups: medication users who were still depressed and medication users who were not.

When they looked at all three groups, depressed medication users performed worse on tests of concentration and scanning than people not on any medication at all. Nondepressed medication users scored somewhere in between.

“It’s still a little bit murky,” says Dannewitz, who performed the study as a graduate student at the University of North Dakota. “My bottom line is that those taking antidepressants with highly depressed mood do perform significantly worse than a control group.”

Her research does have some caveats. The study subjects were taking a variety of different antidepressants—from Prozac, a selective serotonin-reuptake inhibitor, to Wellbutrin, an atypical antidepressant.

They also could have been taking other medication in addition to antidepressants, and a couple of the study subjects were taking up to 10-12 medications, says Dannewitz.

Dannewitz declined to speculate whether the behind-the-wheel behavior she witnessed could lead to more accidents in the real world; she says that previous research into the effect of antidepressant use on cognitive function has been mixed.

Some studies indicate that taking an antidepressant improves cognitive function in the moderately depressed. Others suggest that when people who aren’t depressed take such a medication, they do worse on tests of mental ability.

Investigating the effects of antidepressants and depressed mood on mental performance is important—and not just for driver safety, Dannewitz says.

“Would you really want to have brain surgery [done by] someone who is really depressed, or would you rather have them on an antidepressant, or no medication at all?”

For now, Dannewitz believes the research is too conflicting and preliminary to conclude that not taking antidepressants would be a safer alternative.

“I think my general assumption is, if you have significant depression, then an antidepressant is probably going to help you in your performance,” she says.  “It seems to be a mishmash of mood and medication, and that’s what we need to tease out for future studies.”

By Theresa Tamkins