It's Nearly Impossible to Test for Weed in DUI Cases

The latest episode of 'Weediquette' looks at the issues facing law enforcement and impaired driving.
May 10, 2017, 3:16pm

While cannabis is still stigmatized in parts of the United States, its use has generally become less taboo. Despite our current administration's inaccurate claims about marijuana in relation to the opioid crisis, it seems that Americans are moving toward legalization on a national level.

But the nationwide increase in cannabis use has also resulted in more stoners behind the wheel. Traffic fatalities are the highest they've been in 50 years, and even though there are reportedly fewer drunk drivers on the road, law enforcement believes that other forms of impairment are negatively affecting drivers. There isn't enough evidence to validate this theory in its entirety, but police have reason to be skeptical. How can law enforcement officials prove that a driver is under the influence of cannabis while behind the wheel? At the moment, they can't.


On the most recent episode of WEEDIQUETTE, we meet Greg, a medicinal cannabis patient recently charged with a weed-related DUI in Washington State. While Greg believes he wasn't high when he got behind the wheel, the amount of evidence law enforcement has against him will be hard to refute, regardless of whether or not he was impaired.

Field sobriety tests have proven their accuracy in identifying drunk drivers, but there's little scientific evidence supporting its accuracy in detecting impairment caused by weed. Law enforcement believes marijuana to cause psychoactive hindrance, but the marijuana tests performed by police officers are purely physiological. During these tests, officers will check subjects for a heightened pulse or blood pressure, as well as subtle ticks like eyelid tremors. The final step in justifying whether or not somebody is "too stoned to drive" is a THC blood test performed by a hospital or lab.
Marijuana can remain in the human body for a month, give or take. However, labs typically test for an "active," unmetabolized presence of THC, which allows law enforcement to know whether or not the subject has used marijuana in the past few hours. In Washington State, if the blood test reports five or more nanograms of THC per milliliter of blood, the driver is considered impaired and thus charged with a DUI. Greg, who uses marijuana regularly, tested for 22 nanograms of THC—a seemingly high level for somebody operating a vehicle.

Because Greg smokes a joint a day, his tolerance will naturally be higher than someone who only smokes once a month. Therefore, when Greg claims that he is "completely functional" under the influence of cannabis, it's likely a sincere statement. However, there's no scientifically sound way to test someone's tolerance, since the drug affects everyone differently in different amounts—just like other medications. There are countless across-the-board discrepancies in inhibition and behavior caused by marijuana, making guidelines even harder to establish.

All of these factors make universalizing a limit on behind-the-wheel weed intake nearly nonsensical, calling into question the constitutionality of existing DUI weed laws. "There's decades of data establishing the connection between the presence of alcohol and how it impairs drivers," WEEDIQUETTE host Krishna Andavolu tells us. "For pot, that data is simply not there."

Follow Amelia Capaz on Twitter.

You can watch WEEDIQUETTE on VICELAND. Find out how to watch here.