Criminalizing driving over a specific THC/marijuana blood level ignores the absence of a cause-effect correlation

Fairfax DWI and marijuana defense attorney on the need to reverse the overcriminalization of our society

May 13, 2016 Criminalizing driving over a specific THC/marijuana blood level ignores the absence of a cause-effect correlation

The news has recently been abuzz about the wisdom, or not, of criminalizing a person’s driving with a specific THC (marijuana’s main active ingredient) blood level.

Alec Siegel at Law Street Media says that “drivers in Montana, Washington, Pennsylvania, Ohio, Nevada, and Colorado are convicted of a DUI if they are found with a certain amount of a cannabinoid–THC, hydroxy-THC or carboy-THC–in their bloodstream.” Similarly, East Bay Times says “In 12 states, driving with any trace of marijuana in the body is a criminal offense, and in five others, the presence of a designated amount of marijuana’s active ingredient in a driver’s blood triggers an automatic conviction.”

Recenctly in Michigan, the “House voted 107-1 … on a bill to create a commission to research and recommend a threshold of THC bodily content that would constitute evidence of impaired driving.”

It was bad enough that 2000 federal highway legislation shoved mandatory criminalization of driving with a 0.08 blood alcohol level down the states’ throats under the penalty of otherwise losing federal highway funding. Now we have a slippery slope of governments trying to criminalize threshold THC levels as well.  The whole effort is oversimplification of police, prosecution and judicial work at the expense of those whose driving is simply not made dangerous by a mere threshold level of alcohol or THC in their bloodstream.

As a forensic toxicologist I work with confirms, blood THC levels cannot correlate with any driving impairment. For starters, THC remains in one’s bloodstream for weeks, and marijuana smoked two weeks ago clearly is not going to impair one’s driving today.

Although the hardly liberal American Automobile Association claims that fatal “crashes involving drivers who recently used marijuana doubled in Washington after the state legalized the drug,” AAA also acknowledges and links to studies supporting that legal “limits, also known as per se limits, for marijuana and driving are arbitrary and unsupported by science.”

In 1993, the United States Department of Transportation acknowledged that “[a]vailable evidence leads to the conclusion that it is usually impossible to predict the psychological effects of THC from its determination in a single plasma sample.” “Marijuana and Actual Driving Performance” at 2 (DOT).  Subsequently, the DOT through the National Highway Safety Transportation Administration says: “It is difficult to establish a relationship between a person’s THC blood or plasma concentration and performance impairing effects.” (Thanks to Paul Armentano for his article and links on this subject.)


The United States has become an overcriminalized society that is a far cry from the ideals of life, liberty and the pursuit of happiness expounded jpon in the Declaration of Independence. If we do not make life more of a matter of caveat emptor/buyer beware rather than passing law after law to try to insulate people from others’ actions, we will continue to pay for it with the police-nanny state that we currently have.

  • Ryan C.
    Posted at 01:45h, 15 May Reply

    I love reading these blog entries. Hopefully this particular issue will be transcended with self-driving cars, but my fear is that even more intrusive laws will come on the books so law enforcement can continue to shred our 4th amendment rights. I was so disappointed to read how the Virginian courts upheld the “dangling object” conviction despite no violation. It feels like we’re on a slippery slope where cops will just be able to say they “felt” like someone had broken a law, although they couldn’t put their finger on which one, and that will be enough to uphold what should be an illegal search. I’m surprised an officer’s “gut instinct” isn’t already admissible in court since it would be “unreasonable” for them to clearly know the entirety of the law. But with rulings like we’re already seeing, it doesn’t feel like that future is too absurd or too distant.

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