Male patients had a 38% lower risk of crashes when taking medication, researchers say
Female patients on medication had a 42% lower risk of crashes
Car accidents occur at dramatically lower rates among medicated ADHD patients in the United States than among those not taking medicine, according to a study of more than 2.3 million people published Wednesday in JAMA Psychiatry.
Previous studies have documented a higher number of car accidents among people with attention deficit/hyperactivity disorder.
The symptoms of ADHD, a neurodevelopmental disorder, can include an inability to pay attention, impaired impulse control and hyperactivity, which is often expressed as excessive fidgeting, talking or tapping.
People with ADHD may have problems with one, some or all of the behaviors.
“Core symptoms of ADHD (e.g., inattention and impulsivity) may interfere with the competencies necessary to drive safely, predisposing those with the disorder to greater risk for accidents and injuries,” said Zheng Chang, lead author of the study and a researcher in the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet in Sweden.
People with ADHD who find it difficult to pay attention may be more prone to drive distracted, increasing their chances of a car crash.
Chang and his co-authors estimate that up to 22.1% of car crashes could have been avoided if the patients with ADHD had received medication.
“This is a prevalent and preventable cause of mortality and morbidity among patients with ADHD,” Chang wrote in an email, “and that is an important reason we investigated this issue.”
Driving: A complex task
Using health insurance claims for 2005 through 2014, Chang identified more than 2.3 million Americans over the age of 18 who had ADHD. Of them, 83.9% (more than 1.9 million) received at least one prescription for ADHD medication, and on average, they were about 32 years old.
Chang and his colleagues looked for emergency room visits resulting from car crashes in which these patients were driving during the same period. Then, the researchers compared the risk of a car crash during months when patients had filled a prescription for their ADHD medication with the risk during months when no prescription had been filled.
They found that 11,224 ADHD patients had visited an emergency room after a car accident.
To draw a comparison, the researchers looked at car crash data from a control group: age-matched and sex-matched people who had not been diagnosed with ADHD.
People with ADHD had a higher risk of car crashes than the control group, the researchers found.
Specifically, “male ADHD patients had a 38% lower risk of (motor vehicle crashes) when receiving ADHD medication compared to when not receiving medication, and female patients had a 42% lower risk of (motor vehicle crashes) when medicated,” Chang said.
The researchers acknowledge a few caveats: Their data include only emergency room visits, not fatal accidents or less severe accidents that don’t require medical services. The data include all car crashes, not just those caused by distracted driving; the percentage of total distracted driving accidents to which drivers with ADHD contributed has not been calculated. And finally, a filled prescription does not necessarily mean the medicine was taken.
Worldwide, car crashes claim about 1.25 million lives each year. In the United States, 32,744 people died on the road in 2015, and distracted driving accounted for 3,477 of those deaths, according to the National Highway Traffic Safety Administration.
Stephen Hinshaw, an expert in the field of ADHD who was not involved in the new research, noted that a number of studies have revealed driving safety risks related to ADHD symptoms. In particular, he said, symptoms causing lapses in attention and rash judgments, whether due to hyperactivity or impulse control, have been implicated in unsafe driving behavior.
“This study–of a large population, is of major importance,” said Hinshaw in an email. “The results are compelling. Still, medication for ADHD does not constitute, in most cases, a complete ‘cure.’”
To gain competence as a driver would likely require combinations of medication with psychosocial treatments, such as behavior therapy, Hinshaw said.
According to Dr. Vishal Madaan and Daniel J. Cox, both of the Department of Psychiatry and Neurobehavioral Sciences at the University of Virginia Health System, driving “represents a complex neurobehavioral task involving an interplay of cognitive, motor, perceptual and visuospatial skills.”
This task is not one that all people with neurodevelopmental disorders, such as ADHD, may fully master, they note in an editorial published alongside the study.
‘Practice is everything’
As patients reach adulthood, the natural course of ADHD is a decrease in hyperactivity but persistent inattention and impulsivity, according to Madaan and Cox. Doctors should keep this in mind when considering treatment options, they say, though health care professionals should also be aware that car crashes involving ADHD patients “often happen later in the evening when their medications may have worn off.”