Ross Koplin

Marijuana, the Colorado Driver, and Driving Under the Influence of Drugs (DUID): The Debate Continues

What is the marijuana debate in Colorado as it pertains to drivers?

Marijuana and Colorado Driver | Driving Under the Influence of Drugs

Marijuana and Colorado Driver | Driving Under the Influence of Drugs

As of April of 2013 the Colorado legislature is again struggling with a revision of the Driving Under The Influence of Drugs (DUID) law as it relates to the legality of a person driving with THC in their system. Colorado lawmakers have been attempting to derive a standard measurement of intoxication comparable with that utilized of the comparatively reliable and direct measurement of blood alcohol content when a person is tested for Driving Under the Influence of Alcohol (DUI). Due to the greatly differing nature of marijuana intoxication, and alcohol intoxication, and inherent differences in meaningful measurement technology for the two substances as they effect the human body, it has proven to be very difficult to develop a standard for meaningful measurement of THC intoxication and consequent driving impairment.

Is it illegal to drive under the influence of marijuana in Colorado?

Yes, in Colorado, it is currently illegal to drive while impaired by or under the influence of either alcohol or drugs or a combination of alcohol and drugs. In the event marijuana or other drugs are prescribed to a person, and the person is otherwise entitled to utilize marijuana, or other prescribed drugs, such entitlement may not be used as a defense against such prohibition against driving while a person’s ability is impaired by drugs or that person is under the influence of drugs.

How do prosecutors prove THC impairment?

While Colorado has had testing standards for years regarding Blood Alcohol Content, only recently has the State House of Representatives passed a bill that would implement specific testing standards for delta 9- tetrahydrocannabinol, known more commonly as THC.

THC is the psychoactive ingredient in marijuana and is the chemical responsible for the “high” that smokers of the drug report. The House bill (which has not reached the Senate yet as of April 2013) would permit a jury to be instructed that the jury has the option of adopting the permissive inference that a driver was impaired at the time of their arrest if blood tests show more than 5 nanograms per milliliter (ng/ml) of THC in their blood. In order to become law, the bill would first have to be approved by the Senate and signed by the Governor.

What is the “Per Se” standard applicable to blood alcohol content in Driving Under The Influence (DUI) cases in Colorado?

In Colorado, as in many states, there exists, in addition to other standards, a per se standard for alcohol intoxication for drivers accused of Driving Under the Influence of alcohol (DUI). Presently this standard is 0.08 percentage of alcohol, by volume, in a person’s blood, otherwise referred to as milligrams of alcohol per deciliter of blood. In Colorado, it is a per se misdemeanor for any person to drive a motor vehicle when the person’s BAC is at or above 0.08 at the time of driving or within two hours of driving. A driver can argue that the test was not accurate, or not properly administered, thus rendering it unreliable, however, the driver cannot argue that he or she was not really under the influence of alcohol if a proper test, which results are shown to be presumptively accurate, provide evidence of a percentage blood alcohol content greater than 0.08.

What is “a permissive inference” of impairment?

When a law allows a permissive inference, the jury considers the evidence presented in the case and uses it to make a determination based on the law and the facts of the case. Practically, if the current bill passes the legislature and becomes law, this will mean that a jury may be instructed to consider the permissive inference of guilt if a driver’s test results show the driver had more than 5 ng/ml of THC in their blood. However, unlike the per se standard, the defendant could argue that even with such test results, due to specific circumstances, he or she was not really driving under the influence of THC, or was not driving while their ability was impaired by THC. Otherwise, under the proposed new law, a driver found guilty of driving under the influence of marijuana could be prosecuted in much the same manner as somebody who was convicted of driving under the influence of alcohol.

Is a Driver with 5 ng/ml of THC in their system actually impaired?

This is one of the questions the Colorado legislature is struggling with. When a police officer stops a driver under the suspicion that he/she is driving under the influence of alcohol, the tests administered (blood alcohol and breath alcohol) give results that fairly directly correlate to the driver’s level of impairment. This doesn’t mean that there aren’t lawful ways to fight blood or breath tests, but that the science behind these results, as they relate to impairment, is fairly well established.

With marijuana, unlike alcohol, THC stays in a person’s system after the euphoric effects have worn off. That means that a test may show more than 5 ng/ml of THC in a driver’s blood even though the person, was not, at the time of arrest, driving under the influence of that drug. There is further data to suggest that a person who is a frequent user of marijuana may have higher levels of THC in their system, but lack the same euphoric effect detrimental to the person’s driving ability, as a new user of marijuana with exactly the same level of THC. The lack of an effective, simple test to directly relate the presence of THC in a person’s blood, with a person’s driving impairment, makes real world meaningful testing of THC driving impairment difficult.

Since the presence of THC may not prove impairment, how does the new law handle the difficulty in proving impairment?

Given the substantial limitations of tests for THC, especially the potential for false positives as to likely driving impairment, members of the Colorado legislature are attempting to adopt an objective rule involving a chemical test. However, unlike the per se standard for Driving Under The Influence of Alcohol, the new bill would provide for the permissive inference standard which would thereby allow, but not require, juries to find that a driver was under the influence of marijuana if the test result shows more than 5 ng/ml of THC in their system. It thereby also allows accused drivers to present evidence supporting their position that they were not under the influence, such as evidence that they were not driving recklessly or in a manner that indicated they were unfit to drive. Unfortunately, a lack of an effective test proving conclusive proof, one way or the other, will most likely lead to inconsistent ruling in marijuana cases and is the reason why many defense attorneys have encouraged the state legislature to find a more conclusive testing procedure before enacting laws to prosecute drivers.

Because the state of the law is unresolved, if you have additional questions about the laws surrounding driving under the influence of marijuana or alcohol, please contact Ross Koplin, as an experienced Denver criminal defense attorney he is happy to answer your questions.

Legal Disclaimer – The information contained at this web site is not intended to be legal advice and all information regarding Colorado criminal law is general content only and should not be relied upon for any specific Colorado criminal law situation. Information on this web site is not intended to be comprehensive and does not cover all the issues, nuances or ramifications related to the topic discussed. This web site may not be updated routinely to reflect the very most current Colorado law.

Individuals should consult an experienced Denver criminal attorney, Denver DUI laywer, or Denver traffic lawyer for advice regarding an individual situation. 

by Ross Koplin


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Ross E. Koplin, Attorney at Law

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Ross Koplin is a Traffic Attorney serving the Denver Metro area who provides quality legal representation to those involved in traffic misdemeanors, including prosecution for traffic tickets, speeding tickets, driving under the influence of alcohol or drugs (DUI), or other traffic offenses.

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