Male teenagers with attention deficit hyperactivity disorder are more likely to be injured in traffic accidents than teens without disruptive behaviour disorders, whether they're drivers or pedestrians, new research shows.
The seven-year study of boys aged 16 to 19 was led by Dr. Donald Redelmeier, a professor of medicine at the University of Toronto who has attracted international attention for previous auto crash studies on an increase in fatalities on Super Bowl Sunday and the dangers of talking on a cellphone.
This time, he focused on what he calls the single most risky demographic on the road - teenage boys - whose crash rate is twice that of the general population.
"Our main finding was that a history of ADHD was associated with about a 35 per cent relative increase in the risk of a motor vehicle crash," Redelmeier said Monday as his paper was released in PLoS Medicine, an open access journal that's available online.
"It's a lot, so that if you were to bring teenagers with ADHD down to the same crash risk as teenagers without ADHD, that would save about 700 crashes each year in Ontario."
"My recommendation is that ADHD ought to be listed just like epilepsy, just like diabetes, just like sleep apnea, just like many other traditional medical disorders, that is, individuals have to show themselves under good control if they wish to maintain a driver's licence."
But it's important to note that there was no exploration of who was at fault in any of these accidents. And the authors stress the findings don't justify withholding a driver's licence.
Still, experts in the ADHD community say the study will draw attention to the need for awareness and steps that can be taken to prevent such accidents.
For the study, Redelmeier and his colleagues compared 3,421 male teenagers admitted to Ontario hospitals from April 2002 to March 2009 due to road crashes to a control group of 3,812 male teens admitted for appendicitis.
Using universal health care databases, they were able to determine how many of the traffic accident victims had been treated previously for disruptive behaviour disorders.
"We found that the increase in risk also extended to individuals who were pedestrians involved in a motor vehicle crash, so that even when they're not behind the wheel, they continue to be at increased risk," said Redelmeier, a staff physician at Sunnybrook Health Sciences Centre, Canada's largest trauma centre.
"We think that that's all due to this idea of distraction, and just not paying attention to roadway circumstances."
He noted that about a quarter of a million roadway crashes in Ontario each year result in roughly 800 deaths and about $20-billion in societal losses.
"Teenagers only account for a fraction of the problem ... they number about three per cent of the driving population, yet account for about six per cent of total crashes," he said.
"ADHD only accounts for a sub-fraction of the teenagers, i.e. about five per cent of them, so that it - overall - amounts to a very small slice of a very large pie .... Ontario might save about $60-million in societal costs each year if teenagers with ADHD could reduce their risk to the norm of other teenagers without ADHD."
One of the limitations of the study is that it couldn't determine whether the teens with ADHD were taking medication at the time of their accidents.
But Redelmeier said it's a common concern that kids with ADHD will go off their meds because of side-effects, even though they realize their powers of concentration and awareness are improved by taking the drugs.
Dr. Laurence Jerome, a child and adolescent psychiatrist specializing in ADHD, said stimulant medications improve the brain's ability to be flexible and adaptive and to pay attention in boring situations.
People with ADHD have been monitored with and without stimulants in simulators and on the road, and the medications actually reduce adverse driving events, he said from London, Ont., where he is an adjunct professor at the University of Western Ontario.
"The medicines only work if the people take them. And when it's in the evening and weekends ... we have a compliance problem."
Heidi Bernhardt, national director of the Centre for ADHD-ADD Advocacy, Canada (CADDAC), said some medications taken in the morning will wear off by evening.
"We've now got medications that are lasting longer ... than the older medications, but some of them may not go into the evening enough. So there is potential to use a short-acting medication as well as the one medication they might use during the day to make sure that their treatment is in place when they are driving."
She noted that the study authors say their findings don't justify withholding a driver's licence, "but whether insurance companies can use this to bump up rates further is a concern."
Jerome said it's an important study using hospital-based data of people who've actually had accidents.
"It's really a verification of what we've known, with an epidemiological frame that's not really a biased sample based on clinic studies (in) which ... you never quite know if you're getting a representative sample. So it's a very, very important finding."
And Jerome said it's important to understand that not everyone with ADHD is a problem driver.
However, the study authors said physicians should talk to their patients about ways to reduce risk.
"The recommendations would be all the standard things: specifically, avoid excess speed, restrict the use of alcohol, minimize other distractions as well as always use your seatbelt, maintain safe distances from other vehicles and obey medical advice," said Redelmeier.