Caroline Cassels

May 22, 2009

May 22, 2009 (San Francisco, California) — Studies have shown that the core symptoms of attention-deficit/hyperactivity disorder (ADHD) interfere with safe driving abilities. Although it is known that adolescents with ADHD are more likely to be involved in automobile collisions than teenagers in the general population, older adults with ADHD could also be more prone to auto accidents than people of similar age without the disorder, according to a study presented here at the American Psychiatric Association (APA) 162nd Annual Meeting.

"Normally, people become better drivers as they age. But we found that collisions for males with ADHD steadily increased as they aged," study investigator Richard Merkel, MD, from the University of Virginia in Charlottesville, told Medscape Psychiatry.

By contrast, collisions tended to decline among older female ADHD drivers as they aged — similar to the trend seen in the general population, according to the new research.

In the study, researchers posted a survey for drivers with ADHD on 5 Web sites, including 1 run by Children and Adults with Attention-Deficit/Hyperactivity Disorder, for 6 months.

Two-thirds of those who responded did not complete the survey entirely and were eliminated from the study. Of all qualifying surveys, 156 were completed by males and 283 were completed by females who had been diagnosed with ADHD.

Possible Selection Bias?

Overall, the study comprised 142 adolescents (16 to 18 years), 161 young adults (19 to 25 years), and 136 middle-aged people with ADHD (26 to 62 years). Results indicated that in the previous 12 months, 28% reported receiving a citation, 34% reported being involved in an automobile collision, and 44% reported either a citation or collision.

Middle-aged adult male drivers reported 1.1 automobile collisions in the previous year — a number higher than that in the general population. A similar national survey of the general population reported only 0.06 collisions in the previous 24 months, according to Dr. Merkel.

The researchers concluded that long-acting stimulant medication is needed for ADHD drivers; it has been shown that these treatments improve driving ability.

"Most of the people in the survey were not adequately treated, if at all," Dr. Merkel said.

Although the study is an interesting one, at least 1 expert questioned its validity. "Part of the problem with Internet-based surveys is that people self-diagnose with ADHD. And there may be some selection bias in the study. So the people who responded may be more likely to have problems with ADHD and may thus be more likely to be involved in accidents," said Iqbal Ahmed, MD, from the University of Hawaii, in Honolulu, and a member of the APA Scientific Program Committee.

Ahmed conceded that it is entirely likely that drivers with ADHD are more prone to accidents than the general population, as are patients with cognitive disorders. "Still, I would expect that driving in older people, even those with ADHD, would get better with age. So what they're reporting doesn't make sense to me," he said.

Dr. Ahmed noted that attention is an important factor in driving ability: "It certainly makes senses that those with ADHD would have a higher rate of accidents in general," he said.

The study was supported by a grant from Shire Pharmaceutical. Dr. Merkel and Dr. Ahmed disclosed no relevant financial relationships.

American Psychiatric Association 2009 Annual Meeting: Abstract NR2-042. Presented May 18, 2009.

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