New study shows no significant link between driving under the influence of cannabis and road accidents

A legitimate concern when reforming cannabis laws is its effect on road safety. Proponents of a ban fear that liberalizing cannabis would increase the number of road accidents.

Numerous studies have been carried out on this subject, with more or less conclusive results. The latest, published in the journal Frontiers in Pharmacology, analyzed the most recent research on the subject and concluded that there was no significant link between driving under the influence of cannabis and the number of road accidents.

Researchers at the University of Bucharest in Romania reviewed data from 24 studies that examined the correlation between cannabis-positive drivers and fatal and non-fatal road accidents.

The authors of the study concluded: «our analysis suggests that the overall effect of driving under the influence of cannabis on road accidents is not statistically significant».

Scientists are also questioning the validity of previous studies, particularly on the levels of THC in the bloodstream. «A positive blood test for cannabis does not necessarily mean that the driver is under the influence of cannabis, since the metabolites of cannabis can be found in the blood. THC can be detected in blood long after its use, especially among regular cannabis users, which can lead to a significant bias in the analysis of the results.»

In particular, the study distinguishes between the presence of THC in the blood, the active substance in cannabis which has a half-life of 7 hours, and the presence of THC-COOH, one of THC's metabolites, which remains detectable for several days after consumption.

«Merely identifying cannabis use on a driver is not sufficient to justify the assumption of an increased risk of road accidents,» the study notes. «When such a result is obtained, it should be accompanied by quantitative data on cannabis use,
or a clinical evaluation of the driver, before establishing his or her fitness to drive. »

Although this meta-study does not identify any statistical link, it is estimated that the cannabis use while driving increases the probability of having an accident by 1.65. In the case of alcohol, the probability is 17.8 times greater.