Whenever cannabis legalization is being debated, conservative groups are likely to bring up concerns over whether or not stoned drivers will increase the risk of traffic accidents. Several studies have been conducted on the topic in recent years, but the results have been inconclusive and filled with contradictory results. In a new study published this month in the Frontiers in Pharmacology journal, researchers analyzed the most current research on the issue and found no significant link between stoned drivers and traffic accidents.

Researchers at the University of Bucharest Department of Medicine and Pharmacy conducted a meta-analysis on 24 different studies examining links between driving under the influence of cannabis (DUIC) and unfavorable traffic events (UTEs), including collision, injury, or death. After analyzing the data from all 24 studies with two different meta-analytical methods, the research team found no statistically significant link between cannabis intoxication and an increase in traffic accident risk.

The researchers also identified a number of limitations in the original research studies, most notably the fact that some studies relied on inaccurate blood tests for THC levels. "A positive test for cannabis (i.e. blood) does not necessarily imply that drivers were impaired, as THC/metabolites might be detected in blood a long time after impairment, especially in chronic cannabis users, which could also induce an important bias in the analysis of the results," the researchers wrote.

THC can remain in an individual's system for weeks, and a blood test for THC levels cannot accurately differentiate between a driver who is currently stoned and a driver who is sober but may have used cannabis in the past weeks.

"Simply identifying cannabis use in a driver is not enough to justify the assumption of an increased risk for UTEs," the study concluded. "When such a result is obtained, it should be corroborated with either quantitative data regarding cannabis use, or a clinical assessment of the driver, before establishing his (or her) fitness to drive."

Due to the limitations of the study, further research will need to be performed in order to definitively determine the effects of cannabis use on driving. In Colorado, researchers are using legal cannabis users as subjects for a variety of new studies on the topic. Several studies are currently being conducted where participants are asked to take a variety of driving-related, motor control, and cognitive tests after hitting their own dab rigs or using other cannabis products of their choice.