Study Finds Driving on Marijuana Less Dangerous Than Alcohol

One of the challenges facing lawmakers in states with legal marijuana, medicinal or recreational, is the question of drugged driving.

Regardless of how you feel about the issue, there will be people driving while high on marijuana; when the police pull them over, what should they do? How high is too high? What are the dangers associated with driving while on marijuana? What about when combined with alcohol?

In an attempt to answer that question, a study was conducted at the University of Iowa’s National Advanced Driving Simulator, in conjunction with principal investigators from UI’s College of Medicine and College of Pharmacy.

Published in the journal of Drug and Alcohol Dependence, the study is part of a larger research effort sponsored by the National Highway Traffic Safety Administration, National Institute of Drug Abuse and the Office of National Drug Control Policy.

The study involved 18 participants, between the ages of 21 and 37, who had reported using marijuana or alcohol more than twice a month but no more than three times a week. After consuming alcohol, marijuana, or a placebo, they participated in a 35-45 minute driving simulation where their driving abilities were tested.

While there were various factors used in evaluating each participant’s driving abilities, researchers focused on three main factors: the number of times the car left the lane, weaving within the lane and the speed of the weaving.

Those that consumed alcohol did about as well as you would expect. With a BAC of .065, drivers under the influence of alcohol were more likely to leave their lane and weave within their lane at higher speeds.

Researchers came to the conclusion that those under the influence of marijuana “may attempt to drive more cautiously to compensate for impairing effects, whereas alcohol-influenced drivers often underestimate their impairment and take more risk.”

However, it should be noted that those under the influence of marijuana experienced a tunnel-vision effect and an increase of weaving within their lanes in a manner similar to a driver with a BAC of .08. The THC blood level of participants was 13.1 µg/L.

Participants under the influence of both alcohol and marijuana experienced what researchers called an “additive effect,” causing drivers to weave within in their lanes as often as one under the influence of alcohol or marijuana, despite having a lower blood level of both substances.

So what does this study mean for the marijuana industry?

For one, it highlights the difficulties of crafting drugged driving legislation. In addition to the driving test results, researchers found that marijuana can be detected from saliva but not in a reliable manner.

Andrew Spurgin, a postdoctoral research fellow with the UI College of Pharmacy, explained, “Everyone wants a Breathalyzer which works for alcohol because alcohol is metabolized in the lungs … . But for cannabis this isn’t as simple due to THC’s metabolic and chemical properties.”

Whether it is a blood, urine or saliva test, the current methods of measuring marijuana intoxication are insufficient for the challenges faced by lawmakers and industry members. Additional research will be needed in the coming years so states can make informed policy decisions on legal marijuana and highway safety.

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