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How Can a Prosecutor Prove Impairment in a DUI Marijuana Case?

There are restrictions regarding the use of marijuana across the country. While some states allow it to be used for medical purposes, others have legalized marijuana for recreational use.

While this is true, driving while under the influence of marijuana (just like alcohol) is illegal across the country. Unfortunately, testing for the presence of cannabis isn’t as easy as it is to test for alcohol. As a result, prosecutors must use other methods to prove impairment. Keep reading to learn what some of those methods are.

DUI Marijuana Investigation: Evidence of Impairment

Most DUI arrests begin after a driver is pulled over by the police after they are observed committing a traffic violation. Driver conduct can be used as evidence of being impaired, including when a driver weaves frequently, runs red lights or stop signs, or displays other concerning actions while behind the wheel.

In other situations, there may not be any evidence of impaired driving. For example, if a driver is stopped for equipment violations, such as a faulty brake light or cracked windshield, or if the driver has been stopped at a DUI checkpoint.

During the initial stop, a police officer will talk to the driver and form an opinion regarding if the driver is under the influence of cannabis based on certain objective evidence, including (but not limited to):

  • Driver’s admission of marijuana use
  • Physical symptoms of marijuana intoxication
  • Smell of marijuana

Sometimes, the officer will use a Drug Recognition Expert, or DRE, officer to help with the investigation. These are officers that have undergone specialize training to recognize the signs of drug intoxication. The driver may also be asked to participate in field sobriety testing used for determining impairment.

All the records and tests performed by the officer can be used by the prosecution to prove a driver was impaired.

Chemical Testing

After being arrested for DUI, a driver will be asked to undergo chemical testing. Unlike a driver that’s arrested for suspicion of drinking and driving, DUI marijuana drivers are not given the choice of a blood or breath test. There’s no breath test for marijuana, so a blood test is the only tool available.

The blood test’s results aren’t known immediately, and typically provided at the person’s arraignment as part of the initial discovery packet. The results of a blood test show the concentration of THC in the person’s blood. If the THC levels are high, then the prosecution is going to use this is further evidence of a driver’s impairment level.

Proving Marijuana Impairment

The prosecution in a DUI case involving marijuana is going to use all the information listed above to prove their case and that the driver was, in fact, impaired. As a result, the driver needs to hire an attorney to ensure their rights are protected and that they don’t submit to any testing or other questions that may harm their case and lead to more consequences.


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