Antidepressants Impair Driving Ability? Really?

A couple of months ago I read a few articles about a study that seriously makes me want to scream and throw things. "Antidepressants May Impair Driving Ability, Research Finds" says one headline. My first thought was, "Oh, crud." But then, having years of experience in looking critically at studies, I made sure I read the fine print. Sure enough, there are a few big holes in the logic behind this study.

The research team at the University of North Dakota recruited 60 people to participate in a driving simulation that tested their driving ability in such situations as reacting to obstacles like stop signs or traffic signals while being distracted by things like signs, animals or other cars. Thirty-one of the participants were taking at least one type of antidepressant, while the 29 control group members were not taking any medications (with the exception of oral contraceptives, in some cases). The 31 participants taking antidepressants were further divided into two groups, into those who scored higher and lower on a depression test.

The group of participants who were taking antidepressants and had the more severe depression symptoms performed significantly worse on the driving test than the control group. However, the group who were taking antidepressants but scored low on a depression test performed the same as the non-medicated individuals.

So, to me, there are a few little problems with the conclusions they drew.

• For one thing, depression itself causes problems in concentration. It's one of the major symptoms that many depressed people have. That would account for the fact that the group with the higher number of symptoms of depression performed worst of all, worse than those who were on antidepressants, but not severely depressed. Oh, wait. Here it is - halfway down the page. "However, it appears that mood is correlated with cognitive performance, more than medication use." So tell me, what exactly did this study prove? Nothing, it appears, and nothing about antidepressants affecting cognition.
• Also, how do we know that the group that was taking antidepressants were not taking any other medication that might be causing drowsiness or difficulty concentrating or delayed reaction time? How many medicines have we all taken that warn us not to operate heavy machinery?
• Since there's no mention of the participants getting a full physical before the test, how do we know that there wasn't another physical problem that affected their performance?
• Why didn't the team compare the test scores of people with depression who are on antidepressants to the test scores of people with depression who are not on antidepressants? Or compare the scores of depressed people who are not on antidepressants to the scores of people who are not depressed? Apparently they are going to look at that in a future study. Maybe they realized that their findings are essentially freaking useless.

It's possible that this study eliminated other factors that might be causing the problems while driving, but either they were not included in the press release that the articles were based on, or the article writers did not go into such detail.