Case of the Week: Prosecutors Face Challenges Prosecuting Medical Marijuana DUI Cases

Driving under the influence is always illegal in Arizona, but prosecutors will now have more difficulty pursing DUI cases caused by medicinal marijuana.

The Arizona Court of Appeals recently ruled (12/22/2016) that law enforcement must be able to prove that an alleged DUI offender was too impaired to drive when the impairment was caused by medical marijuana. This case highlights one of the many challenges involved in regulating medical marijuana.

Challenges of Determining Impairment From Marijuana

The evidence necessary to establish impairment is still unclear.  While alcohol has a legal threshold for impairment, marijuana impairment is more difficult to measure. Blood tests are often used to find evidence of marijuana use, but this does not provide clear evidence that the driver was impaired while driving. It also does not provide an objective measurement of the level of impairment.

The state bears the burden of proof in a criminal case.

The December decision by the Court of Appeals highlights that burden and provides some guidance for law enforcement. If an arrest is for impaired driving caused by marijuana, and the driver is a cardholder, the police must assemble evidence to prove that the driver was too impaired at the time they were driving.

Unfortunately, there is no medical consensus on how the level of marijuana in a person’s system determines impairment. A threshold for impairment for one driver may be different from an impairment threshold for another. Blood tests that are taken hours after an arrest do not provide an accurate measurement of what the level of impairment was while driving.

Better testing for impairment caused by marijuana may be developed in the coming years. In the meantime, medical marijuana DUI prosecutions may be “impaired” by limited law and experience in this area.

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