Mark Asbridge Associate Professor Department of Community Health and Epidemiology at Dalhousie Univeristy  Halifax, Nova Scotia

A systematic review based on Cochrane methodology has garnered worldwide attention for a Dalhousie University researcher.

Mark Asbridge, Associate Professor in the Department of Community Health and Epidemiology and the Department of Emergency Medicine, has been interviewed by media giants including the BBC, ABC (Australian Broadcasting Corporation), CNN, CBC, and Reuters, among many others, about his systematic review on cannabis use and motor vehicle collision risk.

The review, Acute cannabis consumption and motor vehicle collision risk: systematic review of observational studies and meta-analysis, was published in the high-profile BMJ (British Medical Journal) in 2012 and revealed acute cannabis consumption is associated with an increased risk of a motor vehicle crash, especially for fatal collisions.

The media took exceptional interest in this information and Asbridge was kept busy for an entire five and half hours one day, completing a series of 10-minute interviews with the CBC alone. “I was interviewed by every CBC station,” says Asbridge, “From Newfoundland to Victoria.”

Asbridge was moved to conduct a systematic review on this topic when he and his colleagues were comparing other primary research with the research they were completing in a hospital setting and there were obvious discrepancies in the literature. “This is an issue that is contentious with evidence on either side, but the evidence hasn’t been weighted. All studies were treated equal when they weren’t,” explains Asbridge.

He decided it would be a useful contribution to the current literature and medical education to conduct a systematic review. It was the rigorous, standardized process that influenced him to use Cochrane methods, acquired through Cochrane Standard Author Training, to complete the review.

The widespread coverage of the research results is welcomed by Asbridge. “All of this brings forward a need to recognize that with the use of cannabis there are a range of consequences, even when used legally,” he explains.

The researcher advises that there is a need to educate younger generations in particular: “There is a large misconception in the 25 and under crowd that cannabis doesn’t impair driving or increase the risk of collision.”

This is especially important as cannabis use continues to rise. Hospital-based studies have shown an increase in use in Canada, the U.S., Australia and some parts of Europe. Those included in these studies were individuals who were in crashes or experienced auto fatalities and had used marijuana.

Asbridge notes that, ironically, while there was previously no other systematic reviews on this topic, two others emerged around the same time his was published; one out of Columbia University and another based

While he acknowledges the results of the reviews are generally consistent, he points out a considerable difference in study measurements. Both the American and Norwegian studies measured cannabis use through urine, while Asbridge included studies in which cannabis was measured in blood. in Norway.

The professor explains the significance: “Blood is more precise. Urine samples don’t measure recent use. They measure use within a 30-day period. Using cannabis a week ago has no bearing on driving today.”

The review has been cited 100 times in the two years since it has been published and it has already influenced some provincial policies and administrative sanctions. It has informed pending changes to the Graduated Driver’s licensing law in Nova Scotia and was used to inform the Canadian Centre on Substance Abuse’s anti -drug and driving campaign. 

The BMJ asked Asbridge to develop Continuing Medical Education (CME) materials for primary care physicians and he was recruited to give a number of talks on the topic to provincial governments (Nova Scotia Departments of Health and Wellness, and Transportation and Infrastructure Renewal) and federal governments (Department of Justice), as well as other stakeholders. Asbridge was even invited to pen an editorial in JAMA Pediatrics this July.

While the review and its results were received positively by many, some were not so keen on Asbridge’s research. CBC’s online article about the review received thousands of comments, some quite negative. “My wife saw the article and said, ‘Don’t read it. Tell your parents not to read it,” laughs Asbridge. “A lot of the comments discredited my research and there were many statements like, ‘I use marijuana all the time and I’m fine.’”

The review was completed with co-authors Jill Hayden and Jennifer Cartwright, both researchers at Dalhousie University, and was funded by the Canadian Institutes of Health Research.