By October 30, 2015 19 Comments Read More →

First of its Kind Study Shows Cannabis Has Little to No Significant Effect on Driving

cannabis and driving

Anna Hunt, Staff
Waking Times

Researchers at the University of Iowa’s (UI’s) National Advanced Driving Simulator (NADS) published a new study that examined how inhaling cannabis affects driving. The results may help shape the rules of how law enforcement handles drivers under the influence of cannabis.

“Alcohol is the most common drug present in the system in roadside stops by police; cannabis is the next most common, and cannabis is often paired with alcohol below the legal limits.

We know alcohol is an issue, but is cannabis an issue or is cannabis an issue when paired with alcohol? We tried to find out.” ~ Tim Brown, associate research scientist at NADS and co-author of the study.

The new study, conducted by Gary Gaffney, Tim Brown and Gary Milavetz, put 18 participants through a 35 to 45 minute simulated driving test, with one group having consumed alcohol, another having vaporized cannabis, and a third group under the influence of both alcohol and cannabis. The effort was sponsored by the National Highway Traffic Safety Administration, National Institute of Drug Abuse, and the Office of National Drug Control Policy.

Four important findings were reported:

  1. Drivers under the influence of only cannabis showed little driving impairment when compared to drivers under the influence of alcohol or both substances.
  2. Drivers with blood concentrations of 13.1 ug/L THC (delta-9-tetrahydrocannabinol, which is the active ingredient in cannabis) showed similar impairment to drivers with a .08 breath alcohol concentration, the legal limit in most states. The current legal limit for THC in Washington and Colorado is 5 ug/L.
  3. Drivers who use alcohol and cannabis together weave more on a virtual roadway than ones that used either substance independently, although consuming both does not double the impairment.
  4. Analyzing a driver’s oral fluids can detect recent use of cannabis although it should not be considered a reliable measure of impairment.

For the study, researchers selected 13 men and five women between the ages of 21 and 37 who reported drinking alcohol and using marijuana no more than three times a week. After spending the night at the UI’s facilities to ensure sobriety, participants were taken to NADS for “dosing” followed by a simulated drive in a 1996 Malibu sedan mounted in a 24-feet diameter dome.

READ: 5 Reasons The Most Dangerous Drug Is Not Illegal

Before the simulation test, each participant had 10 minutes to drink an alcoholic beverage, or a juice with flavoring that mimicked alcohol, and then another 10 minutes to inhale a placebo or vaporized cannabis. The goal was to have some participants’ blood alcohol level at about 0.065 percent, and some participants’ blood concentrations at about 13.1 ug/L THC, and some under the influence of both.

Once in the simulator, drivers were assessed on: weaving within the lane; how often the car left the lane; and the speed of weaving. The researchers reported that drivers with only alcohol in their systems showed impairment in all three areas. They reported that participants only under the influence of cannabis showed impairment only with weaving within the lane.

Andrew Spurgin, a postdoctoral research fellow with the UI College of Pharmacy, shared another important fact as part of the study:

“Everyone wants a Breathalyzer which works for alcohol because alcohol is metabolized in the lungs. But for cannabis this isn’t as simple due to THC’s metabolic and chemical properties.” 

The study’s finding are not likely to have any immediate effect on the current legal limits for THC, but hopefully it will slow the attempts to deploy devices for instant roadside THC testing before further research can be conducted.

Read more articles from Anna Hunt.

About the Author

Anna Hunt is a staff writer for and an entrepreneur with over a decade of experience in research and editorial writing. She and her husband run a preparedness e-store outlet at, offering GMO-free storable food and emergency kits. Anna is also a certified Hatha yoga instructor. She enjoys raising her children and being a voice for optimal human health and wellness. Read more of her excellent articles here. Visit her essential oils store here.


This article (First of its Kind Study Shows that Cannabis Has Little to No Significant Effect on Driving) was originally created and published by Waking Times and is published here under a Creative Commons license with attribution to Anna Hunt and It may be re-posted freely with proper attribution, author bio, and this copyright statement.

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  • Tony van der Veen

    The Dutch did a similar test in the 1990’s. Results were suppressed when it showed that stoned drivers were actually more careful than even unstoned drivers.

  • aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

    Anna Hunt, you’re misinterpreting the statement, “Analyzing a driver’s oral fluids can detect recent use of cannabis although it should not be considered a reliable measure of impairment.” It is NOT saying cannabis doesn’t cause impairment. If you actually read your citation in it entirety it clearly says driving after smoking weed causes impairments to driving similar to alcohol. The sentence you’re misreading is simply saying that testing the driver’s oral fluids for marijuana can only be used to detect marijuana, but can NOT be used to measure whether or not the driver was impaired due to marijuana. It is alluding to the fact that there is not yet a threshold/legal limit for marijuana like the one we have for alcohol (.08% alcohol blood content). If there’s .08% alcohol in your blood, you’re considered too impaired to drive.

  • Ed Hare

    I am an old hippie who can speak from personal experience and say that this article is pure hogwash, and any study that determines that marijuana use does not impair driving is flawed on its face. Like drinking, people can get used to performing some tasks poorly while using, but there were times when cannabis had me hardly knowing which way was up. The present laws are exactly right and no one should be driving either drunk or stoned. No one.

  • Jeffrey Moab

    it actually makes you drive safer….if everyone smoked a joint on the way home i dont think we would have a road rage problem…or…could it be that people are in such a hurry to get home and smoke a joint??? food for thought.

  • Terry Adams

    Actually this ISN’T the first of it’s kind test comparing driving ability to pot intake. Car and Driver magazine famously did the same thing back in the 70’s (or was it the early 80’s..??- I was doing my own pot testing back then, I cannot recall).. Their driving initially IMPROVED…. but later they began to get sloppy behind the wheel, their throttle foot and hands on the steering wheel questioning each directive from their brain…

  • plamenpetkov

    total BS. I drove on weed once long time ago and everything was blurry and im amazed i didnt cause an incident. total BS. problem with the internet is that any type of BS can be published by anybody.

    • Mikkel Kruse

      I smell BS here. To be high is not “all or nothing”.. the same as alcohol there is big differende in HOW high you are when driving.. My experienced guess here, is that you were simply to high to manage it. Weed/cannabis it not for everybody, and how well you tollerate it and manage yourself and how impaired you get when smokine comes down to tollerance, experience, quantity, potency and so on… Never drive under heavy influence, but being a little high is not the same

    • Gene

      ur the one with the BS syndrome guy!

  • davol

    I just got to remember to go the speed limit. I get all relaxed and enjoying the ride until I notice other drivers passing me and giving me dirty looks.

  • Simon Sez

    Field sobriety tests are nothing more than a way for the state to monetize the people some more. They are in no way connected to weather or not a person is at all impaired. Asking someone to recite the Alphabet backwards from Y to H or asking someone to stand on one foot serves as flimsy evidence as to the sobriety of a driver/rider.

    As far as the state is concerned, if the state is going to legalize Cannabis then they need a new revenue stream to replace the current possession laws and so we will end up with field sobriety tests for Cannabis use. Those tests will be as or less accurate than the current road side chemical drug tests which detect almost ANY substance as an illegal drug. Look up false positive results for roadside drug tests if you have not heard about the subject.

  • Yeah. You never hear “Stoned driver kills a bus full of nuns.”

  • Dimitri Ledkovsky

    Some studies have shown that limited alcohol consumption improves a drivers focus and driving skills. You can make a study fit and objective. Same with pot. I, for one, absolutely do not accept that pot doesn’t impair driving and most motor skills. There seems to be a rush out there to market cannabis as a panacea for just about anything and everything. Taking turns, corn, soy beans, “canola”, even petroleum occupied similarly enviable positions. May cooler heads prevail.

    • I’ve driven stoned for most of my life without incident. You never hear reports of stoned drivers causing accidents, EVER!

      • Tuaca1107


      • Bogdanian

        makes it better actually, you are more aware.

      • plamenpetkov

        well we just had one over the weekend in downtown LA where I guy hit 10 people so now you have heard.

        • Gene

          source or its bullshit!

    • Karolyn

      It is a panacea.

    • freewheelinfranklin543

      The actuarials have shown for years that drivers stoned only on grass drive better than those who are sober. That’s why the insurance industry has not been up in arms about legalization. This has been known by the insurance companies for years.Nothing new here.

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