Accident Analysis & Prevention, a peer-reviewed journal, reported in its July 2004 article titled "Psychoactive Substance Use and the Risk of Motor Vehicle Accidents," by K.L.L. Movig, et al.:

“The objective of this study was to estimate the association between psychoactive drug use and motor vehicle accidents requiring hospitalization.

The risk for road trauma was increased for single use of benzodiazepines and alcohol… High relative risks were estimated for drivers using combinations of drugs and those using a combination of drugs and alcohol. Increased risks, although not statistically significant, were assessed for drivers using amphetamines, cocaine, or opiates.

No increased risk for road trauma was found for drivers exposed to cannabis.”

July 2004