- Funding: Insurance Institute for Highway Safety
- Principal Investigator: Cheryl Cherpitel, Subaward; Esther Choo, Oregon Health and Science University, PI
A strong association has been established between alcohol use and motor vehicle collisions (MVC’s), but less is known about cannabis use and MVC or the interaction of cannabis with alcohol and other drugs as a risk factor for such collisions.
The principal psychoactive component of cannabis, delta-9-tetra-hydrocannabinol (THC), has been found to significantly impair attention, reaction time, hand-eye coordination, decision making and concentration, as well as driving performance. The risk for MVC with cannabis, as the most commonly used drug worldwide, and cannabis with alcohol, as the most common co-ingestion, is of particular concern in the current legal environment: 23 states and the District of Columbia (DC) have enacted legislation to decriminalize marijuana for medical use, four of those states and DC have legalized marijuana for recreational use, another four states are likely to do so by the end of the year, and initiatives are pending in others.
The small amount of available literature suggests that cannabis increases crash risk and that cannabis and alcohol have a potentially more-than-additive effect on driving, increasing crash risk. Most of the existing literature, however, examines either MVCs in which no injury occurred, or only fatal crashes in which detailed information about quantity and context of cannabis use cannot be captured.
AIM 1: Examine the prevalence of cannabis use, patterns and context of use among adult drivers presenting after MVC to the ED of Oregon Health & Science University (OHSU).
AIM 2: Using a case-crossover design, estimate the relative risk (RR) of MVC for cannabis use alone and in combination with alcohol, after controlling for context of injury and other drug use.
AIM 3: Analyze the dose-response relationship of cannabis and alcohol use for risk of MVC, quantifying the amount of use through a) serum and ethanol levels obtained on arrival in the ED, and b) interviews regarding use of cannabis (e.g., type, mode of delivery, relative potency, estimated amount) and alcohol, both usual use and use within six hours before the crash event, which will allow us to explore the interaction of usual use on the dose-response relationship.