The high road

Dal professor Mark Asbridge is in the driver's seat for a study on cannabis and collisions. (Danny Abriel Photo)

Impaired driving is one of the leading causes of death in Canada. But how do its dangers change as cannabis use grows in popularity, especially among younger Canadians?

A 2006 study from the Canadian Centre on Substance Abuse found that almost five per cent of Canadians surveyed reported driving within two hours of using cannabis in the previous 12 months, a two-fold increase from similar studies done in the late 1980s. A 2002 Senate special subcommittee concluded that the number may be even higher—up to 20 per cent for young men under the age of 25.

Medical research has shown that cannabis affects drivers differently than alcohol: rather than slowing reaction time, it tends to distort space perception. What concerns Mark Asbridge, assistant professor in the Department of Epidemiology and Community Health at Dalhousie, is quantifying the risk involved when individuals choose to get behind the wheel while high.

“We don’t have a lot of evidence to work with other than self-reporting,” says Dr. Asbridge, noting that existing statistical research relies on either individuals confiding their actions or toxicology samples taken after a fatal accident. “We have self-reporting and we have death – we want to fill in the grey area in between.”

It what he calls “a marriage of my research interests,” Dr. Asbridge will bring his expertise in injury prevention and addictions research to bear on a research project on the relationship between cannabis use and traffic collisions, with the hope of providing Canadian policy makers, academics and the general public with new insight into the issue.

“Our study attempts to get closer to the question of risk,” he explains. “We want to uncover whether people who use cannabis are more likely to be involved in collisions and whether the severity is heightened, and if there’s any synergy between the use of alcohol and cannabis in collisions,” he explains.

The study will take place at three Canadian hospitals: St. Michael’s Hospital and Humber River Regional Hospital in Toronto and the QEII Health Sciences Centre in Halifax. Individuals involved in a traffic accident where cannabis use was a factor will be invited to take part as participants in the study. To overcome the challenge of acquiring a control sample—since drivers who use cannabis but don’t get into collisions are not usually reported—Dr. Asbridge and his team will use a case-crossover design that asks the same test subjects to report past driving behaviour and drug use to expand the research.

Last week, it was announced that Dr. Asbridge’s study is one of several Dalhousie projects to receive funding from the Canadian Institutes of Health Research. CIHR will be providing more than $650,000 towards the research, which will begin once final ethical clearances are achieved. The project aims to survey over 1,500 subjects over two years.

Dr. Asbridge hopes the results they uncover will help Canadians make smart decisions about their driving habits: “Anything we can provide that can help with injury prevention is a good thing.”