Pubdate: Mon, 01 Jan 2007
Source: Canadian Journal of Public Health (Canada)
Copyright: 2007 Canadian Public Health Association
Contact:  http://www.cpha.ca/english/cjph/cjph.htm
Details: http://www.mapinc.org/media/4430
Authors: Bedard M., Dubois S., and Weaver B.
Bookmark: http://www.mapinc.org/mjcn.htm (Cannabis - Canada)
Bookmark: http://www.mapinc.org/find?224 (Cannabis and Driving)

ABSTRACT: THE IMPACT OF CANNABIS ON DRIVING

Background: Cannabis is known to have detrimental effects on human 
performance and may also affect driving adversely. However, studies 
designed to examine this issue have provided equivocal findings. We set up 
this study to further determine the effect of cannabis on driving.

Methods: We used a cross-sectional, case-control design with drivers aged 
20-49 who were involved in a fatal crash in the United States from 1993 to 
2003; drivers were included if they had been tested for the presence of 
cannabis and had a confirmed blood alcohol concentration of zero. Cases 
were drivers who had at least one potentially unsafe driving action 
recorded in relation to the crash (e.g., speeding); controls were drivers 
who had no such driving action recorded. We calculated the crude and 
adjusted odds ratios (ORs) of any potentially unsafe driving action in 
drivers who tested positive for cannabis but negative for alcohol 
consumption. In computing for the adjusted OR, we controlled for age, sex, 
and prior driving record.

Results: Five percent of drivers tested positive for cannabis. The crude OR 
of a potentially unsafe action was 1.39 (99% CI = 1.21-1.59) for drivers 
who tested positive for cannabis. Even after controlling for age, sex, and 
prior driving record, the presence of cannabis remained associated with a 
higher risk of a potentially unsafe driving action (1.29, 99% CI = 1.11-1.50).

Conclusion: Cannabis had a negative effect on driving, as would be 
predicted from human performance studies. This finding supports the need 
for interventions to decrease the prevalence of driving under the influence 
of cannabis, and indicates that further studies should be conducted to 
investigate the dose-response relationship between cannabis and safe driving.
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