States Struggle To Address Issue Of Driving While High On Cannabis

By Lindsey Weedston 01/09/19

Federal legalization could be on the horizon, yet so far no one has come up with a definitive method to determine if someone is too high to drive.

Red and white DUI cannabis stop sign

As more states legalize both medical and recreational marijuana, authorities are struggling to determine the best way to address the issue of driving while high. Unlike alcohol, cannabis can stay in a person's system for weeks after the last time they used – long after the high has subsided and they are no longer impaired. Blood and urine tests are therefore considered by many to be unreliable methods for determining if a driver is intoxicated. 

Marijuana legalization will likely be a key issue in 2019 as Democrats line up to enter the 2020 presidential race. Ten states have now legalized recreational cannabis, and even conservative states like Utah and Oklahoma are starting to pass medical marijuana laws. Federal legalization could be on the horizon, yet so far no one has come up with a definitive method to determine if someone has taken too much of the drug to be able to drive safely.

“You can’t legalize a substance and not have a coherent policy for controlling driving under the influence of that substance,” says Rand Corp. assistant policy researcher Steven Davenport. 

Yet many states are relying on police officers to perform field sobriety tests as their only means of determining if someone is high on cannabis behind the wheel. According to Kaiser Health News, California police are given 16 hours of training on recognizing the influence of various drugs, including cannabis.

The coordinator of this program, Glenn Glazer, claims that California officers are “very used” to recognizing marijuana intoxication, but as Davenport points out, field tests are subjective by nature.

According to the National Conference of State Legislators, the majority of states with some kind of legalized marijuana have “zero tolerance” laws on the books for driving while high, meaning that any amount of THC and/or its metabolites found in a driver's system is grounds for legal action. This presents a serious problem when these chemicals can stay in a person's system for a full month after they last used. 

Source: NCSL

Others have “per se” laws similar to the blood alcohol limit. However, cannabis researchers have repeatedly pointed out that finding a limit for cannabis-related compounds in the blood is much more complicated than with alcohol. There is no clear, linear relationship between THC levels in the blood and intoxication.

Keith Humphreys, a psychiatry professor and drug policy expert at Stanford University in California, believes that the number these states have picked for their legal limit is arbitrary, saying they “made it up.” 

“We don’t really have good evidence — even if we know someone has been using — [to gauge] what their level of impairment is,” says Humphreys.

Coming up with a solution won't be an easy task, but people are trying. In late 2017, an app was released that calculates the user's reaction time. Cannabis often slows reaction time and impairs one's ability to focus, making driving while high a dangerous endeavor. After Washington State and Colorado legalized recreational marijuana, highway collisions rose by 3%, according to the Highway Loss Data Institute

The app, called DRUID, is far from a perfect system for detecting intoxication, but if a blood, urine or breathalyzer test can't be developed soon, field tests and human judgment may be all police have to rely on.

“The idea that you could come up with a completely objective test of performance … is ambitious,” says Carnegie Mellon University drug policy researcher Jonathan Caulkins.

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Lindsey Weedston is a Seattle area writer focused on mental health and addiction, politics, human rights, and various social issues. Her work has appeared in The Establishment, Ravishly, ThinkProgress, Little Things, Yes! Magazine, and others. You can find her daily writings at Twitter: