People with attention-deficit/hyperactivity disorder (ADHD) are more likely to be in a serious traffic accident, but medication may counteract that risk for some, according to a new study from Sweden.
Researchers found that people with ADHD are about 50 percent more likely to be in serious traffic accidents, compared to people without the condition.
But taking medication to control some of the symptoms may help reduce that increased risk - at least among men, according to the study's lead author.
"It has been known for a while that ADHD is associated with traffic accidents and traffic violations," Zheng Chang said. But, he added, "there are no studies from the population level looking at ADHD medication."
Chang is currently at the University of Oxford in the UK, but completed the research while at the Karolinska Institute in Stockholm.
ADHD is a neurodevelopmental condition that results in people having trouble paying attention and controlling impulsive behaviors and being overly active, according to the U.S. Centers for Disease Control and Prevention (CDC).
The CDC says about 11 percent of children between four and 17 years old were diagnosed with ADHD as of 2011. The condition often lasts into adulthood.
For the new study, the researchers used data collected between 2006 and 2009 from 17,408 Swedish adults with ADHD.
During that time, there were about 214 serious accidents among every 10,000 men with ADHD each year. That compared to about 77 accidents per 10,000 men without ADHD.
There were also about 120 accidents for every 10,000 women with ADHD per year during the study, versus about 52 accidents per 10,000 women without ADHD.
The researchers write in JAMA Psychiatry that while they can't say why there appeared to be an increased risk of serious traffic accidents among people with ADHD, past research has attributed it to inattentiveness and impulsivity.
Next, the researchers compared driving data from people with ADHD who had a prescription for ADHD medication to those who weren't prescribed medication.
They found men who had a prescription were 29 percent less likely to be involved in a serious traffic accident.
To eliminate differences between the men included in the study, the researchers compared data from times when each man was on ADHD medication to times when the same man wasn't on medication.
In that analysis, men were 58 percent less likely to be in an accident while they were taking ADHD medication, compared to times when they weren't getting treatment.
For women, however, there was no difference in risk. Chang said the study may not have been able to pick up subtle differences, because fewer women were included.
Overall, the researchers said that between 41 percent and 49 percent of accidents among men with ADHD may have been prevented if they were on medication.
Chang told Reuters Health the findings may actually underestimate the risks of ADHD and the benefits of medication, because his team only looked at serious accidents.
"This is just the tip of the iceberg," Daniel Cox said. "It's only reporting on accidents that resulted in the hospitalization of ADHD drivers."
Cox was not involved with the study but has done research on traffic accidents among people with ADHD. He's also director of the Virginia Driving Safety Laboratory at the University of Virginia in Charlottesville.
He said the study can't say how many people who were prescribed ADHD medications were actually taking them.
"What it says is if you drive and have ADHD, you really have to think of this as something very different from a non-ADHD driver," he said. "That it is a risk."
Cox also said that not everyone with ADHD necessarily has an increased risk of accidents.
"We need to drill down and identify those at risk and focus on those," he said.