Pubdate: Fri, 10 Feb 2012
Source: Windsor Star (CN ON)
Copyright: 2012 The Windsor Star
Contact: http://mapinc.org/url/PTv2GKdw
Website: http://www.canada.com/windsorstar/
Details: http://www.mapinc.org/media/501
Author: Sharon Kirkey
Bookmark: http://www.mapinc.org/find?224 (Cannabis and Driving)
Referenced: Acute Cannabis Consumption and Motor Vehicle Collision 
Risk: Systematic Review of Observational Studies and Meta-Analysis: 
http://www.bmj.com/content/344/bmj.e536

STUDY FINDS POT USE DOUBLES ACCIDENT RISK

Cannabis impairs psychomotor skills for driving

Driving under the influence of pot nearly doubles the risk of a 
serious or fatal car crash, a Canadian study finds.

Cannabis -- marijuana -- is the most widely consumed illicit 
substance in the world, and the number of Canadians confessing to 
driving within an hour of using pot is growing, researchers from 
Dalhousie University write in this week's issue of the British Medical Journal.

In addition, "surveys of young drivers have also shown that rates of 
driving under the influence of cannabis have surpassed rates of 
drinking and driving in some jurisdictions," the Halifax team reports.

Not only is cannabis relatively easy to get, "many young people 
really don't believe that cannabis impairs," said lead author Mark 
Asbridge, an associate professor in the department of community 
health and epidemiology at Dalhousie.

"They know that alcohol impairs their driving, so if they're the 
designated driver at a party they'll switch alcohol for cannabis. 
I've heard stories: 'I'm the designated driver so I'm just going to smoke up.'

"We just simply don't have the same messaging around drugs and 
driving" that exists around drinking and driving, he said.

Past studies into cannabis and crash risk have been mixed.

Some have found an increased risk of being involved in a collision 
after using marijuana, but others have found either no association 
whatsoever, or even a lower risk -- suggesting people were actually 
safer driving while intoxicated by pot than not.

The Halifax team set out to disentangle the evidence. They performed 
a "systematic" review, scouring the literature for the best-designed 
studies they could find.

In the end, they pooled data from nine studies that, combined, 
involved 49,411 drivers from Australia, New Zealand, the United 
States, France and the Netherlands.

All the crashes involved in the analysis took place on public roads 
and involved one or more moving vehicles such as cars, vans, trucks, 
buses and motorcycles.

The researchers found a 92 per cent increased risk -- a near doubling 
- -- of a driver being involved in a collision resulting in serious 
injury or death, to themselves or others, if they used marijuana 
within two to three hours of getting behind the wheel.

The strongest association was with fatal crashes.

The study wasn't designed to answer the question of how much pot it 
takes before crash risk increases.

Most studies in the analysis used any amount greater than zero as the 
cutoff for a positive test result.

But, "for cannabis, there's not necessarily a cutoff that we can 
identify where risk was most heightened," Asbridge said.

Still, studies have shown that cannabis impairs the psychomotor 
skills needed for safe driving, he said.

Marijuana affects perception and spatial awareness.

Drivers have difficulty staying in their lanes, Asbridge said.

"There's actually a psychological process where people often believe 
that they're driving safer than they really are and they don't 
recognize that they're following too closely, or making these lane violations."

Earlier studies that suggested it might be safer driving under the 
influence of cannabis often relied on urine samples. The problem 
there, Asbridge says, is that markers for cannabis in urine "can stay 
in your body for weeks or even over a month, so that's not a measure 
of recent use at all."

His team included only studies that measured active THC metabolites 
from blood samples, which is a more accurate way of measuring whether 
someone has smoked up within the past few hours.

In 2004, four per cent of Canadian adults reported driving within one 
hour of consuming cannabis, up from 1.9 per cent in 1996-97.

According to the 2009 Canadian Alcohol and Drug Use Survey, 11.4 per 
cent of Canadians overall, and 33 per cent of 15- to 24-year-olds 
reported using marijuana at least once in the previous year, the 
Halifax researchers note in the journal.

Governments in Australia, western Europe and the U.S. have introduced 
roadside testing for cannabis that uses a saliva test, instead of a 
breath test, to detect recent pot use, Wayne Hall, of the University 
of Queensland Centre for Clinical Research in Australia, writes in an 
accompanying editorial.

But more research is needed to determine whether random roadside 
drug-testing reduces pot-related road crash deaths, he said.

In Canada, specially trained police use a 12-step test that looks for 
"biomarkers" -- dilated pupils, for example, or sweaty palms and 
elevated heart rate -- to detect drug-impaired drivers, Asbridge said.

Some jurisdictions in Europe have a zero-tolerance approach.

"So if any measured level is in your system, you're guilty," Asbridge said.

Nearly two-thirds of Canadians are open to the idea of 
decriminalizing or legalizing marijuana, according to the results of 
a recent poll.

At its recent biennial policy convention in Ottawa, the federal 
Liberal party voted overwhelmingly to support legalization of the drug.
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MAP posted-by: Jay Bergstrom