Driving Under the Influence of Non-Alcohol Drugs--An Update Part I: Epidemiological Studies.

Epidemiological studies of the association between drug use and involvement in road traffic crashes (RTCs) published from January 1998 to February 2015 have been reviewed. Cohort andpopulation studies compared RTC involvement among drug users and non-drug users, case-control studies compared drug use among RTC-involved and non-RTC-involved drivers, and responsibility studies and case-crossover studies were performed for RTC-involved drivers. Difficulties associated with the types of studies are discussed with a special focus on case-control studies. Statistically significant associations between drug use and RTC involvement were found for benzodiazepines and z-hypnotics in 25 out of 28 studies, for cannabis in 23 out of 36 studies, for opioids in 17 out of 25 studies, for amphetamines in 8 out of 10 studies, for cocaine in 5 out of 9 studies, and for antidepressants in 9 out of 13 studies. It was a general trend among studies that did not report significant associations between the use of these drugs and increased RTC risk that they often had either poor statistical power or poor study design compared to studies that found an association. Simultaneous use of two or more psychoactive drugs was associated with higher RTC risk. Studies on the combination of alcohol and drugs have not been reviewed in this article even though this combination is known to be associated with the highest RTC risk.