Portland, OR: The use of alcohol, but not cannabis, is associated with greater odds of suffering a motor vehicle crash requiring emergency care, according to case-control data published in the journal Accident Analysis and Prevention.
A team of investigators from universities in California, Colorado, and Oregon examined the relationship between cannabis and alcohol use and incidences of motor vehicle collisions (MVC) among patients admitted to emergency departments.
They determined that those who either self-reported or tested positive for the use of alcohol alone possessed a crash risk that was more than twice (OR = 2.50) that of controls (those who tested negative). By contrast, those who either self-reported or tested positive for cannabis possessed a lower risk of accident (OR = .80) than controls.
Those patients who either self-reported or tested positive for the use of both alcohol and cannabis in some instances possessed a higher risk of accident than those who used either substance alone. That finding that is consistent with several prior studies, but others have failed to report this outcome.
Authors concluded: “This was a cross-sectional study of visits to EDs [emergency departments] in Denver, CO, Portland, OR, and Sacramento, CA by drivers who were involved in MVCs and presented with injuries (cases) and non-injured drivers (controls) who presented for medical care. … Our study supported an increased risk for MVC among those with acute alcohol and combined alcohol and cannabis use. Some of our findings suggested an absence of added odds or even reduced odds for MVC among those using cannabis alone prior to driving. … Overall, our study reinforces that in this era of increased liberalization of cannabis, emphasis on actual driving behaviors and clinical signs of intoxication, rather than specific drug-level thresholds, to determine driving under the influence has the strongest rationale.”
NORML has long opposed the imposition of per se THC thresholds for motorists and has alternatively called for the expanded use of mobile performance technology like DRUID to determine whether someone is under the influence.
Full text of the study, “Risk of vehicle collision associated with cannabis and alcohol use among patients presenting for emergency care,” appears in Accident Analysis and Prevention. Additional information is available from the NORML Fact Sheet, ‘Marijuana and Psychomotor Performance.’