Drivers testing positive for the presence of THC in blood do not possess a significantly increased risk of being responsible for a non-fatal motor vehicle accident, according to data published in the journal Addiction.
Investigators from the University of British Columbia compared the likelihood of crash responsibility in drivers testing positive for THC and/or other substances as compared to drug-free drivers over a six-year period (2010 to 2016).
Researchers reported, “In this multi-site observational study of non-fatally injured drivers, we found no increase in crash risk, after adjustment for age, sex, and use of other impairing substances, in drivers with THC less than 5ng/ml. For drivers with THC greater than 5ngml there may be an increased risk of crash responsibility, but this result was statistically non-significant and further study is required. … Our findings … suggest that the impact of cannabis on road safety is relatively small at present time.”
By contrast, authors reported, “There was a significantly increased risk for drivers who used alcohol, sedating medications, or recreational drugs others than cannabis.” Drivers who tested positive for the concurrent use of cannabis and alcohol possessed a higher risk of accident as compared to drivers who tested positive for alcohol alone – a finding that is consistent with other studies.
The abstract of the study, “Cannabis use as a risk factor for causing motor vehicle crashes: A prospective study,” is online here. Additional information is available in the NORML fact-sheet “Marijuana and Psychomotor Performance.”