Study Analyzes How Much Cannabis Impairs Drivers

A federal study has attempted to compare impairment levels for people who smoke cannabis alone, drink alcohol alone or consume a combination of alcohol and cannabis. The results were released in June in the journal “Drug and Alcohol Dependence”.

The study examined drivers’ ability to stay in their lane after consuming alcohol, smoking pot or a combination of smoking and drinking. The study found that combined use impairs drivers more than just one or the other. In addition, the study found that marijuana impairs a novice user’s ability to drive safely, even taken in small quantities, whereas heavy marijuana users showed fewer effects.

The study also found that people with 13.1 nanograms per liter of THC, the active ingredient in marijuana, in their blood had similar driving impairment to someone with a .08% blood-alcohol level.

The study may be used to support those lobbying for mandatory per se limits to be adopted by states for DUI cases based on marijuana. Colorado and Washington have set their limits already at 5 nanograms per liter.

The study was based on the driving of volunteers at the University of Iowa, in a simulation intended to mimic the look and feel of everything from urban parking lots to dark gravel roads as well as unexpected hazards such as swerving cars. Each of the 18 drivers who completed the tests after taking six combinations of pot and alcohol gave blood and saliva tests to check intoxication levels. A 19 th subject was discounted from the study because the person drove badly whether sober, drunk or high!

In California, there is no legal level above which a person is presumed to be impaired through cannabis to drive. However, it is common for prosecuting agencies to charge drivers with DUI based solely on cannabis use, even though these cases may be difficult to prove in court.

If you have been arrested for DUI based on cannabis use or other drug use, please contact Gold & Witham for a free case evaluation.


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