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Taking the High Road: The Facts on Marijuana-Impaired Driving

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Taking the High Road: The Facts on Marijuana-Impaired Driving

Image via TheStonerCafe

Image via TheStonerCafe

Image via TheStonerCafe

Image via TheStonerCafe

Bryden Smith, Counter-Culture Reporter

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Since the legalization of recreational marijuana here in Colorado, driving high has been a major safety concern. Everyone wants their roads to be safe, and considering that drunk drivers are involved in a quarter of fatal accidents, preventing the intoxicated from driving is extremely important.

But how does one define impairment from pot? How can you tell whether or not someone is too high to drive?

The fact is, studies regarding the actual impairment of pot smokers are often conflicted and remain inconclusive. Moreover, a safe and fair standard of measuring how stoned someone actually is continues to evade scientists and law enforcement alike.

Tetrahydrocannabinol (commonly abbreviated as THC), the psychoactive ingredient in marijuana, is limited to five nanograms per milliliter of blood for Colorado drivers. While this is a great starting point, what everyone needs to realize is marijuana and alcohol are not the same substance, and probably shouldn’t be treated like they are. Five nanograms of THC is going to have totally different behavioral effects on people of different tolerance levels. A couple puffs from a joint isn’t going to affect Snoop Dogg, but it might send Attorney General Jeff Sessions into a red-eyed whirlwind.

via Imgur

A 0.08 BAC (blood-alcohol content) works great as a legal limit for drunk driving because, even accounting for variances in tolerance, alcohol effects everyone pretty much the same way. In addition, alcohol is one of the only drugs to completely pass through the blood brain barrier (BBB).  This means that the concentration of alcohol in the blood or breath is an accurate representation of what’s in the brain.

But here’s the thing: THC and most other drugs don’t work like that, making accurate levels of “high-ness”, or impairment, really hard to measure. THC can remain in the body for days — even weeks — after use, which is why testing blood, urine, or saliva isn’t practical when assessing if someone is currently impaired.

As if this issue wasn’t already complicated enough, there are thousands of strains of marijuana, all which can be smoked, vaporized, put in an edible, or turned into a concentrate. They all have different levels of THC, and unlike alcohol, using an exact amount is almost impossible. Even the differences between using a sativa or an indica, the two main types of marijuana plant, can be dramatic. Although most strains today are a hybrid of the two, sativas induce a ‘head-high’ while indicas produce more of a relaxing, body-high.

On the more optimistic side, according to a study done by the National Center for Biotechnology Information, “most marijuana-intoxicated drivers show only modest impairments on actual road tests,” and “experienced users show almost no functional impairment.” In contrast to alcohol users, high drivers tend to drive slower, follow further behind, and become more conscientious of traffic rules.

That doesn’t mean that driving all “stoney-boloney” is okay.

In fact, until more research is done on the actual impairment-effect of marijuana and how to measure it, enthusiasts should be even more careful when getting behind the wheel. We want our roads to be free of unnecessary danger, but we also don’t want smokers who are fine to drive to be punished unjustly. In the past, there have likely been a lot of unfair convictions due to a blood or urine test, which could be picking up THC particles from days prior.

Unfortunately, we may never find a perfect way to measure weed-impairment.

Luckily, an Oakland, CA based company, HoundLabs, is working diligently developing and testing a marijuana breathalyzer. The company values safety and fairness, and is attempting to create a product that can not only measure the amount of THC in the body, but how recently it got there. The product will double as an alcohol breathalyzer, and will reportedly pick up THC particles from smoke and edibles.

Currently, they’re working to make their devices more rugged and sturdy for law enforcement officers.

Still, the use of these devices is pretty controversial because the exact relationship between THC and actual impairment still can’t be quantified. On the plus side, they are far less invasive than blood and saliva tests and will at least limit a portion of unfair arrests.

We are still in the baby steps of understanding marijuana and the effects it has on health, society, and vehicular-impairment, but new research is taking place every day.

Until we know more: puff, puff, park.

How do you feel about driving while stoned?  Let us know in both the anonymous poll and the (non-anonymous) comment section below.

Do you believe you could drive while marijuana-impaired?

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7 Responses to “Taking the High Road: The Facts on Marijuana-Impaired Driving”

  1. Michael Milburn on February 17th, 2017 7:09 am

    All these breathalyzers measure exposure to marijuana, not impairment.
    You should know about the new app called DRUID (an acronym for “DRiving Under the Influence of Drugs”) that I have developed for the iPad and the iPhone, now in the App Store (Android coming soon). DRUID measures reaction time, decision making, hand-eye coordination, time estimation and balance, and it takes just 5 minutes (and we are testing a 2-minute version). Our website is

    DRUID was recently featured on NPR’s All Things Considered:

    After obtaining my Ph.D. at Harvard, I have been a professor of psychology at UMass/Boston for the past 39 years, specializing in research methods, measurement and statistics.

    Michael Milburn
    Department of Psychology

  2. Dr. Denise A. Valenti on February 17th, 2017 8:03 am

    Thank you for your comprehensive and objective comments.

    Bottom line: Designate a driver…call a cab….hire uber
    We know so very little about the impact of marijuana on humans because as a federal Schedule I drug, it is deemed dangerous and thus medical research of “no value”. This has created such a problem in moving the science forward. That said JAMA recently reported that chronic users have a dysfunction in retinal ganglion cells…These cells are critical to accurately process motion, speed, depth and contrast. All important functions for safe driving. The same researchers found that these cells are significantly impaired with acute/recent use of marijuana. IMMAD – Impairment Measurement Marijuana and Driving is a test under development that is a simple two minute tablet application to determine fitness to drive with marijuana use. It capitalizes on the retinal visual impairments caused by marijuana use. It is a direct measure of functions that when impaired result in poor and dangerous driving abilities.

  3. Bryden Smith on February 18th, 2017 11:59 am

    @Dr. Denise A. Valenti, Thank you Dr. Valenti for your insightful reply. During my research, I found similar findings in regards to cognitive studies on the impairment effect of marijuana. The trouble is, often the experimental research differs from what the cognitive studies predict. With so many variables in constant flux, what we really need is research, research, research. It’s a shame our government classifies it as schedule 1, it’s such a roadblock for furthering knowledge. All I want is hard, scientific facts, because the media image is SO skewed–on both sides of the political spectrum.
    Thanks again for your comment!

  4. Dr. Denise A. Valenti on March 11th, 2017 6:19 pm

    @Bryden Smith, Had not responded…my apologies. I agree with your comments. Science, studies and objective research. there is good with marijuana and there is bad.

  5. Joe Dro on February 17th, 2017 5:27 pm

    My subconscious motor functions improve with the use of marijuana. Anything from driving to shooting pool. Not just unimpaired, better.

  6. Bryden Smith on February 18th, 2017 12:03 pm

    @Joe Dro, there are a lot of people I know that share your feelings here. I believe that if that can be scientifically quantified, our government should recognize that. The problem is that not everyone feels the way you do. So far, 38% of the readers who have taken the poll consider themselves unfit to drive while high. Thanks for your comment!

  7. Michael Milburn on February 19th, 2017 5:12 am

    @Joe Dro, There is now an app I developed that you can use to demonstrate that your motor functions improve after using marijuana. Now in the App Store for the iPad and iPhone, D.R.U.I.D. (an acronym for “DRiving Under the Influence of Drugs”) measures reaction time, hand-eye coordination, decision making, time estimation and balance, and integrates the measurements into an overall impairment score. See more at
    After getting my Ph.D. at Harvard, I have been a professor at UMass/Boston for 39 years, with a specialty in research methods, measurement and statistics.

    Michael Milburn, Professor
    Psychology Department

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