Alcohol, marijuana and visual capacity at the wheel

Alcohol and cannabis (marijuana) are the most consumed psychoactive substances in the world, with cannabis being the illegal substance most detected in people behind the wheel in Spain (7.5%). In other nations, the prevalence of this drug is also notable.

These substances have a negative effect on the visual system, an essential system for a highly visual task such as driving.

Scientists from the Department of Optics at the University of Granada (UGR) in Spain have examined the extent to which both substances negatively affect vision and driving. To do this, they analyzed the effect of ingesting two doses of alcohol on vision and driving, using a driving simulator made up of three panoramic monitors, a steering wheel, pedals, a gear lever and the corresponding software.

In this study, the participants consumed, in two different sessions, 300 and 450 ml. Granada red wine with an alcohol content of 13.5%. The average blood alcohol level reached by the participants for both doses was 0.19 and 0.33 mg/l, respectively, the latter being above the legal limit for driving in Spain (0.25 mg/l). In addition, the effect of cannabis on marijuana smokers was also studied. Both the blood alcohol level and the consumption of cannabis were controlled with the devices normally used by the General Directorate of Traffic (DGT).

The visual results obtained by Sonia Ortiz Peregrina’s team showed that both alcohol and cannabis produce a deterioration in contrast sensitivity (ability to distinguish light-dark contrast) and stereopsis (depth vision), as well as an increase in of the diffusion of light inside the eye, favoring the sensation of a luminous veil in visual perception. In general, these visual outcomes were worse for subjects who used cannabis than for those who used alcohol.

Alcoholic beverages, like marijuana, alter mental processes, worsening the visual capacity of the person. (Illustration: Amazings/NCYT)

These two substances also negatively affected the ability to drive, especially the stability of the position of the car on the road and the use of the steering wheel, so that after consumption of these substances there was a greater variation in the position of the vehicle on the road. track with respect to the center of it, as well as a greater fluctuation in the turns of the steering wheel.

The ability to drive was more affected by alcohol consumption than by cannabis, especially when the concentration was above the legal limit for driving in Spain (0.25 mg/l). In addition, a relationship was seen between vision results and driving results under the use of these substances, indicating that those subjects who had worse vision results after the consumption of alcohol or cannabis, drove worse.

These results highlight the importance of making drivers aware of the danger associated with the consumption of certain substances such as alcohol or cannabis while driving.

The new study is titled “Comparison of the effects of alcohol and cannabis on visual function and driving performance. Does the visual impairment affect driving? And it has been published in the academic journal Drug and Alcohol Dependence. (Source: UGR)