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The Fallacy Of The “Marijuana DUI”

Recreational marijuana is becoming legal throughout the US. As it becomes more common, states are facing bureaucratic growing pains.

One of the biggest issues is how to properly identify and regulate stoned drivers. Currently there are no standardized testing methods for marijuana impairment.

A lack of peer-reviewed, federally funded studies on cannabis has made it difficult to address this problem. As a result, lawmakers and courts are struggling to accurately address marijuana DUIs.

Marijuana’s History in America

Marijuana faced gradual prohibition in America starting in the early 20th century. It was outright illegal in every state by the mid 1930’s. A decriminalization movement began in the 70s, leading to medical marijuana in certain states. In 2012, Colorado and Washington became the first states to legalize recreational marijuana.

Cannabis is now legal for recreational use in eight states and medical use in 20 states. More states have legalization bills on the ballot.

Unfortunately, decades of prohibition mean that there aren’t many federally funded and peer-reviewed studies on the plant. The lack of scientific research surrounding the effects of marijuana make laws surrounding its consumption tricky. To put it plainly, we still don’t fully understand how cannabis works, particularly when driving is involved.

Stoned Driving Statistics

The Washington Traffic Safety Commission studied 1,773 fatal accidents that occurred between 2010 – 2014:

  • 60% of drivers tested positive for alcohol, pot or other drugs.
  • Only 8% of drivers involved in fatal accidents tested positive for only marijuana
  • 12% tested positive for the presence of marijuana in addition to another substance. 

These statistics aren’t conclusive. More information is needed to establish any trends between marijuana and driving.


How Marijuana DUIs Work

There are two common ways authorities use to test for a marijuana DUI:

  • Per se DUI laws: Per se laws set a THC threshold limit. Marijuana’s psychoactive property is THC. It’s what makes users feel ‘high.’

Generally, this limits five nanograms of THC per milliliter of blood. Drivers with higher THC levels are considered “under the influence.”

This approach treats cannabis like alcohol. Due to the differences in how marijuana affects the body, there are issues with this method:

1. The limit impacts people differently. A seasoned user would be less impaired on five nanograms of THC than someone using for the first time.

2. THC traces remain in the body for weeks. Even if you haven’t recently used any cannabis, you could potentially fail a Per Se DUI test. Alcohol, on the other hand, dissolves within hours.

3. A universal method for testing for marijuana has not been developed. Unstandardized test methods are error prone.

4. Per se tests do not consider whether or not a driver is impaired. Instead, they focus on the THC levels.

  • Effect-based DUI’s: Unlike a THC threshold test, an effect-based DUI test tries to establish if a driver is impaired or not. Law enforcement will look for clues of marijuana use and conduct a field sobriety test. Like per se tests, there currently isn’t any science backing the validity of these tests.

This approach works for alcohol. But marijuana is different. Its users don’t give off the same clues that drunk drivers do like slurred speech, decreased motor skills, and the smell of alcohol.

Additionally, we still don’t know enough about how marijuana impairs people. This is especially true when accounting for different levels of tolerance. As a result, effect-based tests aren’t reliable in a court of law.

Why is it hard to test drivers for marijuana?

  • Lack of reliable testing methods

The current scientific understand of how marijuana affects our bodies is still unclear. Until we have more research and certainty on the actual impacts, it’s tough to conclusively test.

Counties use different testing methods: urinalysis, blood draws, saliva swabs, field sobriety tests, and more. It’s hard to prove the validity of these tests. The lack of uniformity across states makes for discrepancies in how we test and prosecute stoned drivers.

  • THC is fat soluble

Since THC is fat soluble, it dissolves in a person’s fat cells. This means the process runs slower than something like alcohol, which is water-soluble. The slow process means you can fail a THC test days or weeks after consuming marijuana. This means although THC is found in the driver, that doesn’t necessarily mean their driving skills were impacted by it.

  • Two different forms of THC

There are two different forms of metabolized THC: hydroxyl-THC (11-OH-TH) and carboxy-THC (THC-COOH). 

Hydroxy-THC is the psychoactive metabolite of THC. This is the compound of the plant that makes you stoned. In contrast, carboxy-THC is not psychoactive, and it stays in your system longer.

Most tests looking to detect sobriety search for any THC, not just the active hydroxy-THC. If a test detects THC, it may very well be carboxy-THC. This doesn’t indicate the individual was actually driving impaired. Failing an alcohol breathalyzer, on the other hand, means alcohol is currently in your system.

For infrequent versus frequent users of marijuana, the variance in how long you would test positive can range from four to 12 weeks depending on the quantity as well as frequency of use. With such a wide gap, it’s easy to see why determining intoxication is so difficult. It’s difficult to charge someone with a DUI unless you can prove the reckless driving was a result of being inebriated.

Why it’s hard to Prosecute for DUIs

With marijuana only recently having become legal, there isn’t much case-law to reference. The spreading legalization of marijuana has only just begun, and there is still a lot of discrepancies in standards across states. Between the different laws and lack of central testing method to reference, prosecution is challenging. There are many ways an attorney can poke holes in a case, with improper testing and faulty procedures. Police forces aren’t fully trained or equipped yet to deal with marijuana DUI’s.


As more and more states legalize cannabis, we will gain a greater understanding of how it interacts with human body. New studies and peer-reviewed research will improve our approach to identifying stoned drivers. Several companies are working to create a reliable testing method for weed intoxication. Always remember the best way to avoid getting a DUI is to only ever drive while sober.

Related Reading: Top Ten Marijuana Myths That No One Should Believe
Chelsea Salvador
Chelsea is an undergraduate student, with a passion for business, hiking, and coffee. She believes in the conscious consumer, so she writes to better educate the average American.

2 Replies to “The Fallacy Of The “Marijuana DUI”

  1. What about sugar and caffeine and nicotine and sudafed and nyquil and and and.. All that shizz can impair your driving.

    Was there any information regarding fatal accidents with NOTHING in their system? Curious to see how close to 8% that would be. Seems incomplete without including that info. Almost purposefully….

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