Driving Under the Influence (DUI) of Marijuana

Currently, 23 states have legalized the use of medical marijuana. But while there is less stigma attached to using marijuana these days, many fear that its widespread use will result in more harm than good to society. One of the strongest arguments against increasing the accessibility of marijuana stems from the fear that those under the influence would be dangerous to others should they get behind the wheel of a car. This danger arises because, despite the research showing that high drivers "tend to be more aware they're impaired than alcohol users,” their reaction time slower.[1]  Because of the dangers high drivers pose to the public, law enforcement agencies and policymakers are working to find a way to accurately correlate a person’s level of impairment—and, thus, their inability to safely operate a motor vehicle—to the amount of THC, the active ingredient in marijuana, in their system similar to the ways in which they can with alcohol.

Research by Marilyn Huestis, of the National Institute on Drug Abuse, has shown that when “a smoker's blood THC level peaks at 13 nanograms per milliliter, [the driver] could be just as a dangerous” as a drunk driver.  As a result, policymakers are eager to find methods to quickly assess a driver’s THC levels.  To date, both Washington and Colorado have passed legislation criminalizing driving with more than 5 nanograms of THC per milliliter in their blood.[2]

As it stands now, if a law enforcement officer suspects a person has been operating a motor vehicle under the influence of marijuana one of two methods can be used to determine the levels of marijuana in the driver’s system: blood test or salvia test.  Both have their issues.

First and foremost, blood tests can take weeks to yield results.  But even then, questions about the reliability of blood tests to infer a driver was impaired remain. Blood tests can detect marijuana in a person’s system several weeks after the drug has been used, but the test is not reliably able to prove how much THC a person ingested in the hours just before driving.  Also, the frequency with which a person uses the drug can affect a person’s ability to eliminate the drug from their bodies.[3]  Generally, occasional smokers can clear the drug from their system within hours, whereas chronic users end up accumulating so much THC in their fatty tissues that it could take weeks for the THC to dissipate.[4] Research has also shown that consuming marijuana in an edible form results in only small amounts of THC making it to the blood stream.[5]  Additionally, “[i]t's been proven you can still measure THC in the brain [where it would cause impairment] even if it's no longer measurable in the blood.”[6]

Then, to complicate matters, because chronic smoking of marijuana “reduce[s] the density of cannabinoid receptors," smokers can end up being “cognitively impaired for up to 28 days after their last use, and their driving might also still be impaired for that long.”[7]

The saliva test is considered relatively cheap and easy to use; as a result, legislation has recently been introduced in California which would allow the police to use a small, hand-held device to test for THC.[8] However there is one major drawback: there are products on the market designed with the sole purpose of helping users beat saliva tests by neutralizing the toxins in a person’s mouth.[9]  Further, Dale Gieringer, director of the California branch of the National Organization for the Reform of Marijuana Laws, notes that saliva testing “is still an unproven technology… Its accuracy has not been demonstrated in controlled, published scientific studies. There's no evidence that oral swab testing results have any correlation to impaired driving.”[10]
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Should you be charged with driving under the influence of marijuana, a qualified attorney can help you fight the charges. 


[1] Angus Chen, Why Is It So Hard To Test Whether Drivers Are Stoned? (NPR) 2/9/16

[2] Angus Chen, Why Is It So Hard To Test Whether Drivers Are Stoned? (NPR) 2/9/16

[3] Angus Chen, Why Is It So Hard To Test Whether Drivers Are Stoned? (NPR) 2/9/16

[4] Angus Chen, Why Is It So Hard To Test Whether Drivers Are Stoned? (NPR) 2/9/16

[5] Angus Chen, Why Is It So Hard To Test Whether Drivers Are Stoned? (NPR) 2/9/16

[6] Angus Chen, Why Is It So Hard To Test Whether Drivers Are Stoned? (NPR) 2/9/16 (quoting Marilyn Huestis, of  the National Institute on Drug Abuse.)

[7] Angus Chen, Why Is It So Hard To Test Whether Drivers Are Stoned? (NPR) 2/9/16

[8] Patrick McGreevy, Driving while high? Lawmakers want police to be able to check (LA Times) 4/6/2016.

[9]  Ultra Kleen Salvia Cleansing Mouth Wash and Clear Choice Saliva Neutralizing Gum  are two examples.

[10] Patrick McGreevy, Driving while high? Lawmakers want police to be able to check (LA Times) 4/6/2016.