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Colorado Drivers Smoking Marijuana: How High Is Too High?

For the third time, Colorado legislators have voted down passage of legislation that would institute an acceptable legal limit of THC in the blood of drivers. Most people recognize THC as the active chemical in marijuana that creates a feeling of being high. Colorado State Senator Steve King has argued to have it put back on the ballot again for a fourth go-round.  And so the debate over marijuana use in Colorado continues.

Both businessmen and legislators are grappling with a variety of marijuana-related issues within the Coloradan borders. Three major issues revolve around the use of marijuana for medical purposes, the licensure of dispensaries for medically indicated marijuana, and the possible legalization of marijuana for use by any and all interested parties—parties being an operative word, in this case.

Regarding the measurement of THC in blood levels of drugged drivers, proponents of the legislation state that passage of the law would make it easier to convict someone of drugged driving when there is a blood test taken after an arrest. If the person carried a level of THC at or above 5 nanograms per milliliter (ng/ml) of THC in the blood, he could be convicted of the crime.

But when it comes to driving and use of marijuana in Colorado, the question continues to be: Just how high is too high? The National Highway Traffic Safety Administration offers a Marijuana Performance Fact Sheet that indicates a difficulty in correlating a person’s THC blood level with an actual level of use. The amount of marijuana ingested or inhaled is not the only consideration.

The person’s overall pattern of use as well as the concentration of THC in the marijuana—in other words, how good is the dope?— comes into play. There is also a difference between the THC concentrated in the inhaled marijuana and the THC that will show up as a metabolite in the blood or urine of a person who uses marijuana regularly.

The inhaled THC rises to its peak concentrations rapidly, while the person is still smoking. However, the THC measurable in the blood decreases almost just as quickly. Statistics in a white paper prepared on Drugged Driving for the White House’s National Institute on Drug Abuse demonstrated that 61 percent of drugged drivers who were tested 30 to 90 minutes after smoking had THC concentrations below 2 ng/ml.  This was accounted for by a delay from the time a driver was stopped for possible drugged driving until a blood test could be administered. 

Since the blood THC level declines rapidly, some say that King’s legislation might pass if the legislation established a much higher standard than 5 ng/ml.  Some suggest that an acceptable level of nanograms per milliliters should be set at 10. Such a measurement would indicate a significant level of impairment at an interval 90 minutes prior to the arrest.

Opponents say that people who are cleared to smoke marijuana for medical reasons would be targeted. The bill was amended to exempt medical marijuana users, and that amendment failed also.

Nevada and Ohio permit a measurement of 2 ng/ml in arrested drivers. Nevada, it is noted, has laws approving medical marijuana use, and Ohio does not. The Pennsylvania Department of Health has established a 5 ng/ml limit; while that level has not been legislated, the Department of Health standard has been introduced in drugged driving cases.

In the meantime, many people suggest that no level of THC measurement can be as relevant as a person’s failure to demonstrate acceptable control of his motor functions if he is stopped for possible drugged driving. Senator King insists that his main purpose is to stop somebody who is impaired from getting behind the wheel. He states that over the past four years, traffic fatalities of all types in Colorado have decreased but traffic fatalities related to marijuana have increased by 50 percent.  And so as lawmakers consider this and other bills brought to the legislative table, marijuana use in Colorado goes on.


Join Together Staff. Colorado Lawmakers Reject Marijuana Blood Limit for Drivers. http://www.drugfree.org/join-together/drugs/colorado-lawmakers-reject-marijuana-blood-limit-for-drivers

White paper on Drugged Driving for the National Institute on Drug Abuse, http://www.whitehouse.gov/sites/default/files/ondcp/issues-content/drugged-driving/nida_dd_paper.pdf (page 13).

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