Marijuana, Alcohol and Driving

Here are two studies from Great Britain that are very unlikely to ever appear on the websites or in the literature of the Drug Enforcement Agency (DEA) or Office of National Drug Control Policy (ONDCP). First, researchers at the University of Birmingham’s School of Psychology sought to determine whether or not cannabis use would enhance the negative effects on driving ability produced by alcohol consumption.

The study tested two groups, infrequent cannabis users and regular users of cannabis matched for other factors such as age, gender, alcohol use, and other drug use. They were given both alcohol and placebo then tested on a standard computerized tracking system used to evaluate various drugs effect on driving ability. The participants were required to track a moving target while a variety of distractions appeared on the screen. Both groups performed much better on the placebo as opposed to alcohol.

Conventional wisdom holds that impairment would be increased in the regular users, “but alcohol caused a significant deterioration in performance among infrequent cannabis users relative to regular users.” The investigation concluded: “For psychomotor skills relevant to driving, chronic cannabis use (in the absence of acute administration) does not potentiate the effects of alcohol. In fact, the superior tracking accuracy of regular users relative to infrequent users after alcohol, and their lower scores for dizziness, suggest that chronic cannabis use may instead confer cross-tolerance to specific effects of alcohol on behaviour.”

Secondly, there is work done at Middlesex Polytechnic also looking at the cannabis drinking combination. Both marijuana smokers and nonsmokers were matched for alcohol use and then had their peripheral vision, an essential driving skill, tested. The authors discovered that the “cannabis users were less impaired in peripheral signal detection than non-users while intoxicated by cannabis and/or alcohol” and deduced that the “findings suggest the development of tolerance and cross-tolerance in regular cannabis users and/or the ability to compensate for intoxication effects.”

Cross posted on the Trebach Report