ADHD Medications Reduce Risk for Motor Vehicle Crashes

Batya Swift Yasgur, MA, LSW

May 12, 2017

Use of medications for treating attention-deficit/hyperactivity disorder (ADHD) may reduce the risk for motor vehicle crashes (MVCs), new research shows.

A team of researchers led by Zheng Chang PhD, of the Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden, found men with ADHD had a 38% lower risk for MVCs in months in which they received ADHD medication vs months when they did not receive medication. Women showed a 42% lower risk.

The researchers estimated that more than one fifth of the MVCs involving patients with ADHD could have been avoided had the patients received medication during the entire follow-up.

"The association between ADHD and MVCs is driven by the core symptoms of ADHD — inattention, inattention, hyperactivity, and impulsivity — as well as by problems that frequently co-occur with ADHD, such as excessive risk taking, poor control of aggression, and substance use," Dr Chang told Medscape Medical News.

"ADHD medications have beneficial effects on core ADHD symptoms that increase the risk of MVCs," he said.

The study was published online May 10 in JAMA Psychiatry.

Previous Research "Not Clear"

Earlier studies have associated ADHD pharmacotherapy with improved driving or reduced risk for MVCs, the authors write. For example, pharmacotherapy improved driving performance in virtual reality driving simulations involving people with ADHD.

A Swedish population-based study found that ADHD medication use was associated with lower risk for traffic crashes in men, although the association in women was "not clear," the authors note.

Prescribing practices differ in Sweden and the United States, so data from Swedish studies may not accurately reflect the relationship between MVCs and ADHD medication use in the United States. And previous studies have not clarified whether ADHD pharmacotherapy will lower MVCs on a long-term basis. For these reasons, "additional population-based studies in the United States are needed to evaluate the effect of ADHD medication use on MVCs," the authors note.

To expand upon these previous findings, the researchers followed a national cohort of individuals with ADHD ( aged 18 years or older) during a 10-year period (January 1, 2005, to December 31, 2014) using data from US-based commercial healthcare claims. Outcome events were defined as emergency department (ED) visits for MVC claims.

The cohort consisted of 2,319,450 patients with ADHD (1,121,053 men and 1,198,397 women; mean age, 32.5 [SD 12.8] for the whole cohort), who were observed for a total of 50,667,665 person-months.

To account for confounding by indication when examining associations between ADHD medication use and risk for MVCs, the researchers used a within-individual design for their study and also estimated the population-attributable fraction (PAF) of MVCs in patients with ADHD that resulted from lack of medication treatment.

Patients were defined as having ADHD on the basis of diagnosis, as defined by ICD-9 ADHD code, or the receipt of ADHD medication. The index date was defined as the date of the initial diagnosis or the date at which the first prescription was filled.

The researchers followed each patient either from the index date or from age 18 years, whichever occurred later, until the first disenrollment or the final study date, whichever occurred first. "Disenrollment" was defined as "zero days of medical or drug coverage in a given month."

ADHD medications included amphetamine salt combinations, atomoxetine hydrochloride, dexmethylphenidate hydrochloride, dextroamphetamine sulfate, lisdexamfetamine dimesylate, methamphetamine hydrochloride, methylphenidate, and methylphenidate hydrochloride.

The researchers created a monthly person-time data set to compare the risk for MVCs during months in which patients did or did not receive ADHD medications. They compared the risk for at least one MVC between patients with ADHD and matched control persons.

Preventable MVCs

During the follow-up, 83.9% of patients (n = 1,946,198) received one or more prescriptions for an ADHD medication, and a total of 11,224 patients (0.5%) had one or more ED visits for an MVC event.

Patients with ADHD were found to have significantly higher risk for an MVC than matched control persons (odds ratio [OR], 1.49; 95% confidence interval [CI], 1.46 - 1.54 for men; OR, 1.44; 95% CI, 1.4 1 -1.48 for women). Compared with medicated ADHD patients and control persons, unmedicated patients with ADHD had the highest risk for an MVC event.

At the population level, compared to unmedicated months, the months with ADHD medication were associated with a 12% lower risk for MVCs in male patients and a 14% lower risk in female patients (OR, 0.88; 95% CI, 0.84 - 0.93 and 0.86; 95% CI, 0.82 - 0.90 respectively).

"More importantly," the researchers note, the findings of within-individual analyses were similar. Men with ADHD were 38% (OR, 0.62; 95% CI, 0.56 - 0.67) and women with ADHD 42% less likely to have MVC events during medicated vs unmedicated months, corresponding to a PAF estimate of 22.2% and 22.1%, respectively.

These findings suggest that "within an individual (ie, after controlling for all unmeasured static and measured time varying confounding factors), ADHD medication use was associated with a significant reduction in the risk of MVCs," the investigators write.

The researchers found comparable decreased MVCs in patients at different ages and different index dates. Findings were also similar when they included broader definitions of MVCs (eg, motorcycle accidents).

The researchers call their study "the initial one to clarify the association between ADHD medication use and decreased MVCs in a large sample of women with ADHD," stating that the association was "as strong as that in men."

The study was also the first to examine this association in a US-based population.

The study’s hypothesis was that ADHD pharmacotherapy could reduce MVCs by addressing core symptoms of ADHD and reducing unsafe driving, and "our findings were in line with our hypothesis," Dr Chang said.

Risk Not Confined to Adolescents

Commenting on the study for Medscape Medical News, Vishal Madaan, MD, of the Department of Psychiatry and Neurobehavioral Sciences, University of Virginia Health System, Charlottesville, said that the study "confirms and corroborates existing literature on the role of judicious use of ADHD medications in potentially decreasing MVCs in individuals with ADHD.

"This information is especially important in the adolescent and young adult population that may be more susceptible to suffer such consequences with distracted driving," said Dr Madaan. He is the coauthor of an accompanying editorial and was not involved with the study.

The study was "unique" in "capturing a large cohort of individuals and pursuing their data from a very interesting standpoint, a visit to the ED for an MVC," he observed.

He noted that "probably the biggest limitation of the study is the fact that most vehicular accidents don’t lead to an ED visit and are sorted out by the roadside, implying that the study would likely underreport the optimal benefits from managing ADHD symptoms while driving."

Nevertheless, the study has "pretty clear, important take-home messages," he emphasized.

"Clinicians need to be very mindful of the fact that driving involves a complex cognitive-motor task, and individuals with poorly managed ADHD may have pronounced deficits in executive functioning that may make them more prone to motor vehicle accidents," he said.

Additionally, "it is important to keep in mind that about 50% of individuals with ADHD continue to have symptoms related to inattention as adults, and so dismissing ADHD as being limited to school or college may have terrible consequences."

He cautioned, "At the same time, one needs to be aware of duration of action of the medications while driving, as well as their potential for abuse."

Dr Chang said that adverse effects of ADHD medication cannot be determined from this study and that the findings "should be considered along with other potential benefits and harms associated with ADHD medication."

The study was supported by grants from the Swedish Research Council and the National Institute of Mental Health.

Dr Chang was supported by the Swedish Research Council for Health, Working Life And Welfare. Study coauthor Henrik Larsson, PhD, has served as a speaker for Eli Lilly and Shire and is recipient of a research grant from Shire outside of the submitted work. Dr Madaan has received research support from Forest, Purdue, Medgenics, Sunovion, and Pfizer, royalties from Taylor & Francis (Routledge), and travel support from the American College of Psychiatrists.

JAMA Psychiatry. Published online May 10, 2017. Full text, Editorial

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