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Colorado Law on Driving Under the Influence of Marijuana Takes Effect


A new law that sets legal limits on marijuana levels in the bloodstream took effect in Colorado on May 28. Under the new law, drivers are assumed to be impaired if their blood test shows a level of THC—the active ingredient in marijuana—of 5 or more nanograms per milliliter.

Josh Lewis, a spokesman for the Colorado State Patrol, said the new law will not significantly change how police handle stops for driving under the influence. More officers will be trained in drug recognition, he said.

There is no broadly accepted consensus on how much marijuana a person must consume before they are impaired, The New York Times reports. Some critics of the law say the 5-nanogram threshold is too low because medical marijuana users always have some THC in their blood. Others argue the blood test used to measure THC levels is too intrusive. Washington state has also imposed a 5-nanogram limit for THC for drivers.

The National Highway Traffic Safety Administration is studying the effects of marijuana on drivers, the article notes. Results are expected in late 2014.

6 Responses to this article

  1. Darren / June 30, 2014 at 4:05 pm

    Typical push to legalize before thinking this through. I predicted the actual “law” of recreational pot would be the thorn in their side. If it were up to me I would equate pot use to any drug that impairs driving. You can get a DUI for using certain allergy medicines or any medicine that warns not to operate heavy machinery. For Colorado many pot smokers will easily be arrested for DWAI (driving while ability impaired) because the officer making the arrest will be the only requirement for proof.

    I think it’s a form of justice for putting the cart before the horse. Taking risk before doing your research is also subject to a greater review by the Supreme Court I think. If I were a Colorado or Washington St. resident I would sue.

  2. Leah / May 21, 2014 at 11:05 am

    The half live of Marijuana is 7 days so it takes two weeks to clear a normal individual. If you are a habitual smoker the average amout of THC in the system potentially doubles when you partiake if more than every two weeks. The screening cut of rate reccomended by the Substance Abuse and Mental Health Services Administration (SAMHSA, USA) is 50 ng/ml to screen for “ambiant” exposure. The impared cut off rate for Colorado at 5 ng/ml. Obviously the representatives passing this bill should have done a little more research before passing and putting the 5 ng/ml imparement rate into law.

  3. Betsey / June 17, 2013 at 10:59 am

    This is the nightmare I perceive happening in any state that legalizes marijuana. Now those states will have all sorts of people in jail for driving under the influence of marijauna. Yep, it stays in your system longer, and if you use a lot it will be detected for a while. So it is possible that a person who smoked two weeks ago will be determined to be “legally” under the influence two weeks after use. Wow, I have to say that if I got into an accident with another car in Colorado or Washington, I would demand a test of the other driver. I’d have a decent chance of him/her having THC in his/her system and then the accident would be that person’s fault (if it wasn’t actually anyway).

  4. Shattah206 / June 14, 2013 at 2:12 pm

    1) Because alcohol has a high affinity for water — and human beings are mostly water — breath, blood, saliva (and brain) alcohol are extremely close to equivalent at any time. This is why a breath alcohol test is accurate enough to be accepted in court. Marijuana, on the other hand, is stored in fat cells. Completely different physiology.
    2) Blood tests are typically not administered roadside.
    3) My guess is that the arrest will be for “suspicion of” because they won’t have instant results.
    4) Aspirin is not consciousness-altering.
    5) The other drugs you listed have not been legalized for recreational use. You can be arrested for driving under the influence of any consciousness-altering substance if you demonstrate probable cause. Or, in most states, for driver inattentiveness (tiredness).
    6) Coffee? Really? I think I’ll go grab another cup now.

  5. joebanana / June 12, 2013 at 5:41 am

    Do suspected drunk drivers have to take a blood test? Are these “tests” administered roadside? What is the definition of “impaired”? Is a confirmation test also performed before an arrest? What’s the limit for aspirin? Cough syrup? Paxil? Valium? tiredness? Heroin? Coffee?

  6. Doug / June 17, 2013 at 11:31 am

    Hey Betsey I’d like to point out that the metabolites of THC that are detected in urine have NOTHING to do with intoxication, which is a function of active THC in the blood hence the blood test for impairment. States have been arresting and prosecuting stoned drivers for years, and this new law adds little in terms of safety or common sense. Probable cause for stoned driving still includes driving ten mph or more under the limit in CO so make sure you drive really fast when you come here :)

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