IS THERE A CORRELATION BETWEEN MARIJUANA USE, VEHICLE
CRASHES?

Blood to Be Taken From Injured Drivers in Bid to Answer
This

Injured drivers taken to B.C. hospitals over the next five
years will help answer the question: Do those who are high on
marijuana cause more crashes than sober drivers?

In the marijuana-impairment study -- the first of its kind in Canada --
injured drivers will not be asked permission before their blood is
collected. Since the data is collected anonymously and not used to
pursue legal charges, researchers don't have to seek approval from
drivers to analyze their blood under the ethics-approved terms of the
study.

Blood is drawn for treatment of any injuries and the excess amount is
then analyzed. The sample is assigned a code that is not shared with
police, and the resulting data is then linked to police accident
reports to eventually show researchers if cannabis contributed to the
accident.

A recent random sampling of B.C. drivers showed that 10 per cent were
impaired by alcohol and 7.2 per cent by drugs, usually marijuana or
cocaine. Concentrations of THC, the active ingredient in cannabis, are
what will be measured in the study, which is led by Dr. Jeffrey
Brubacher, an emergency doctor at Vancouver General Hospital.

After alcohol, cannabis is the most widely used intoxicating substance
in the world; in the aforementioned B.C. survey it accounted for about
two-thirds of the drugs detected after police roadside stops (followed
by cocaine). Many marijuana users think it's less hazardous because
cannabis tends to make people drive more slowly and less aggressively
than, say, drivers who are drunk on alcohol, according to studies.
But, at the same time, drivers high on marijuana have a harder time
staying within lanes and their reflexes are slower, which means they
are more likely to crash into obstacles that suddenly appear. On the
other hand, "cannabis users tend to overestimate their impairment
whereas people who used alcohol underestimate theirs," Brubacher
stated in an explanation of his study in the B.C. Medical Journal.

Brubacher said data on the first 100 injured drivers have already been
collected for the study, which aims to include information on 3,000
crashinvolved drivers at five B.C. hospitals.

THC levels in blood -- which are measurable no matter how the cannabis
is consumed (smoked, sprayed, drunk, or eaten) -- yield a blood THC
concentration considered more accurate than THC metabolites in urine.
Brubacher said urine metabolites remain active for days after cannabis
exposure.

"Our primary objective is to determine whether injured drivers who
used cannabis before a motor vehicle accident are more likely to have
caused the crash than those who did not," said Brubacher, adding that
the number of crashes caused by impaired drivers will be compared to a
control group of drivers who were found to be not culpable.

The ultimate goal of the $1-million study, funded by the federal
Canadian Institutes of Health Research, is to help traffic-safety
experts develop safer driving policies.

It is possible, for example, that the study might show whether there
should be a legal cutoff level for THC blood concentration, just as
there is for alcohol.