Combination of Severe Depression and Antidepressant Use Impairs Driving Ability

A combination of severe depression and antidepressant use may impair driving ability, new research suggests.

In a study presented here at the American Psychological Association 116th Annual Convention, researchers from the University of North Dakota found individuals with severe depression who were taking antidepressants had reduced concentration and slower reaction times behind the wheel than their counterparts with milder depression who were also taking antidepressants.

Furthermore, study participants with mild depression who were taking antidepressants performed no differently from normal controls. "These findings suggest that together, high depression scores and antidepressant use seem to confer a double whammy, so that individuals with this combination have significantly poorer concentration and slower reaction times when driving," principal investigator Holly Dannewitz, PhD, told Medscape Psychiatry.

Conflicting Findings

According to Dr. Dannewitz, a small number of previous studies suggest some antidepressants can negatively affect individuals' cognitive performance, impairing memory and reducing reaction time. However, she added, other studies suggest antidepressant treatment has no effect on cognitive function.

To further explore the potential impact of these medications on cognitive function, and specifically driving performance, the researchers recruited 60 individuals — 31 who were on at least 1 antidepressant and 29 matched controls who were taking no medication with the exception, in some cases, of oral contraceptives.

To determine depression levels and information about current medication use, all participants completed the Beck Depression Inventory, 2nd ed (BDI-II), a History of Sadness Questionnaire, and a medical history questionnaire.

Subjects in the antidepressant group were further divided into 2 groups, 1 with average BDI-II scores of 0 – 12 and the other with above-average BDI-II scores of 14 – 39.

Study subjects participated in a computerized driving simulation to assess driving ability — specifically, steering, scanning, and concentration. Following completion of practice laps, individuals completed 4 test laps. The practice lap was the easiest and the final lap the most difficult in terms of a greater number of distracters and the need for more responses.

The driving simulator measured reaction times for 2 tasks — a peripheral and central task. The central task required subjects to hit the brake pedal in response to brake lights, while the peripheral task required participants to hit a paddle in response to a stop sign or traffic signal.

Driving Ban Not Warranted

Interestingly, said Dr. Dannewitz, there were no differences between any of the study groups in terms of their steering/tracking ability. However, the more "subtle" measures of reaction time were where individuals with high depression scores performed poorly.

Although patients with high depression scores who used antidepressant medications did worse than the other 2 study groups, Dr. Dannewitz said the impairment is not so severe that it would warrant a driving ban in such individuals.

Nevertheless, she said, physicians with patients who fit this profile should be aware that their driving ability and other functions that require optimal concentration and quick reaction time may be impaired.

Further research is warranted to tease out whether mood or medication use is the primary driver of this phenomenon or whether there may be a synergistic effect at play. It would also be useful, she said, to investigate different types of antidepressants to uncover potential differences between classes of antidepressant mediations or individual drugs.

American Psychological Association 116th Annual Convention: Abstract I-11. Presented August 17, 2008.

Reviewed by Ramaz Mitaishvili, MD

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