People with attention deficit hyperactivity disorder (ADHD) are already at increased risk of motor vehicle accidents, but it is significantly reduced when they are taking ADHD medication, a 10-year study finds.
The researchers estimate that one in five of the vehicle accidents among more than 2 million people with ADHD during the study period could have been avoided if these individuals had been receiving medication the entire time.
"The patients should be aware of the potential risk of (motor vehicle crashes), and seek specific treatment advice from their doctors if they experience difficulties in driving from their condition," said lead author Zheng Chang, of the Karolinska Institute in Stockholm, Sweden.
Chang told Reuters Health that motor vehicle crashes claim the lives of over 1.25 million people around the world each year.
ADHD is a common disorder with symptoms that include poor sustained attention, impaired impulse control and hyperactivity, he added.
Past studies have found that people with ADHD are at an increased risk for crashes, and that medication may reduce symptoms and ultimately improve driving skills.
To examine the risk of crashes with ADHD and how it is influenced by medication, the researchers analyzed U.S. commercial health insurance claims between 2005 and 2014.
They identified 2,319,450 people over age 18 with an ADHD diagnosis, half of whom were over 33 years old. About 1.9 million of them received at least one prescription to treat their ADHD during the study period.
There are a number of medications used to treat ADHD, including the brand names Adderall and Dexedrine.
Overall, 11,224 people in the study had at least one emergency department visit for a motor vehicle crash. Compared to people without ADHD, the researchers found men with the condition had a 49 percent increased risk of being in a crash and women had a 44 percent increased risk.
When the researchers looked at data for each individual with ADHD, they found the men's risk of motor vehicle crashes dropped by 38 percent during months when they received prescriptions to treat their ADHD. Similarly, women's risk fell by 42 percent during months when they received a prescription.
The study team estimates that 22 percent of accidents among people with ADHD that occurred during the study period wouldn't have happened if every individual had been on medications the entire time.
The reduced risk among people being treated for ADHD was consistent across all age groups and was not largely influenced by other medication use, the authors note in JAMA Psychiatry.
Chang said the results can't explain why people treated for ADHD have a reduced risk of crashes, but there are a few possible explanations.
"It could be due to alleviation of the core symptoms of ADHD (inattention, hyperactivity, and impulsivity), as well as to control of problems that frequently co-occur with ADHD, such as excessive risk taking, poor control of aggression, and substance use," Chang said by email.
"I think with psycho-stimulant medications, we’re oftentimes concerned about side effects and the potential for abuse, but the focus on those risks can sometimes distract from the benefits people get from the medication," said Dr. Jonathan Posner, an associate professor of psychiatry at Columbia University Medical Center in New York.
Other studies show the benefits of treating ADHD with medications, he added. For example, one found that people treated for ADHD had a lower risk of incarceration.
"Psycho-stimulants can reduce some of the really negative consequences of ADHD and really help people with ADHD lead safer lives," said Posner, who was not involved with the new study.
The main concern with ADHD medications is abuse, he noted, but the risk is small if the drugs are taken as prescribed.
In an editorial accompanying the study, Dr. Vishal Madaan and Daniel Cox, of the University of Virginia Health System in Charlottesville remind clinicians treating ADHD patients that inattention and impulsivity symptoms may persist into adulthood. The need to manage ADHD extends beyond the needs of school and workplace, and crashes often happen later in the evening when medication wears off.
"Individualizing and optimizing ADHD pharmacotherapy, while being mindful of adverse effects and the potential for abuse, is the most prudent way forward," they write.