Cannabis use does not impair driving performance, according to a study funded by the State of California

Scientists at the University of San Diego, California, have published a study according to which being under the influence of cannabis is not associated with poor driving performance.

Published May 26, the study was funded by the State of California and involved specially trained law enforcement officers.

After consuming cannabis via a « marijuana cigarette »"containing 5.9 mg of THC or 13.4 mg of THC, or a placebo, the 191 participants assessed their ability to drive using a driving simulator and a real car, and were also subjected to standardized field sobriety tests (FSTs) by specially trained police officers.

Saliva samples were collected at the same time the driving was evaluated, including the ability to stay straight, over a period of 5 hours.

Although the sobriety tests conducted by police officers correctly identified participants in the cannabis control group in 81% of cases, they also incorrectly identified 49% of the placebo group participants as being intoxicated, suggesting a lack of reliability in the tests performed by the police. The officers conducted several tests, including walking and turning, a Romberg test, and standing on one leg and touching the nose with a finger.

The analysis performed by researchers on oral swabs, blood samples, and breath of participants after using the car and the simulator revealed no link between sub-standard driving and cannabis consumption.

Researchers stated in their study: «In the largest trial to date involving experienced cannabis smokers, there was no correlation between THC (and related metabolites/cannabinoids) in blood, oral fluid, or breath and driving performance. The complete absence of a relationship between the concentration of the centrally active component of cannabis in blood, saliva, and breath is strong evidence against the use of laws per se for cannabis.

These results are consistent with a recent meta-analysis according to which THC concentrations are «relatively poor indicators of cannabis-induced impairment.».