DUI and marijuana, how does law enforcement know you're stoned while driving?

Posted by Matt McLane | Oct 10, 2019 | 1 Comment

As marijuana use becomes more prevalent in the U.S. after several states passed the "recreational use" laws, DUI-D (DUI from drug use) will likely become a more common charge filed in courts throughout the country.  As it turns out, the Federal government is encouraging the states to enact laws aimed at prosecuting DUI-D drivers.  The 2012 National Drug Control Strategy Report "encourages states to pursue enhanced legal responses, such as "per se" (or zero tolerance) laws." The Limiting Unsafe Cannabis-Impaired Driving (LUCIP) Act, a bill introduced in March 2014 and again in June 2015 by Rep. Jared Polis of Colorado, would require states that allow use of recreational or medicinal marijuana to enact "per se" THC limits for DUI of marijuana.  In 2014, this bill died in the subcommittee on Highways and Transit.  It was sent to committee again in 2015.  In much the same way that Congress force-fed the .08 BAC legal limit to the states in the mid 80's, this bill would tie highway funding to the passage of "per se" marijuana laws.

Even advocates of marijuana legalization are supporting lawmakers to pass these "per se" weed laws. In Washington state, a compromise between legalization advocates and opponents led to a ballot measure that linked legalization to the enactment of "per se" marijuana DUI legislation.   As part of this compromise, Washington established a "per se" threshold of THC of 5 nanograms per milliliter (ng/mL) of blood (alcohol limit is 0.08% BAC).  A similar compromise occurred in Colorado.  Their bill setting "per se" DUI limits for THC at 5 ng/mL failed three times, until the fourth try, when it passed simultaneously with Amendment 64, legalizing recreational marijuana use in the state.  Colorado is perhaps more appropriately labeled as a modified "per se" state, as a blood test of 5 ng/mL "gives rise to permissible inference that the defendant was under the influence." 

The obvious issue in these DUI-D cases is the idea of required blood draws in order to test for the presence of THC.  Blood draws are a highly contested area of search and seizure laws and allowing law enforcement to request and demand a blood draw on a first-time offender will cause problems for officers. A warrant will likely be required unless the driver consents to the blood draw.  Some jurisdications may not have a judge available to authorize the warrant.  Furthermore, is this standard of 5 ng/mL truly indicative of impairment?  Doesn't THC metabolites remain in the blood for several weeks post consumption? This area of the new DUI-D law will be ripe for litigation and since Kansas has NOT passed a "per se" DUI statute, then prosecutors can not rely on the blood test alone.  Like any other DUI case, they must offer clear evidence of impairment outside the realm of science: Walk and turn, One leg stand, and counting tests are all tools that officers use for a typical DUI investigation.  It will be interesting to see if Kansas follows Colorado and enacts a DUI-D statute that criminalizes driving with THC levels in excess of 5 or more ng/mL.   

About the Author

Matt McLane

Matt McLane was born in Topeka, Kansas, and moved to Pittsburg, Kansas in 1980 where he attended middle school, high school and college. Upon graduation from PSU in 1992, Matt moved back to Topeka where he attended Washburn University law school. Upon graduation, he moved to Overland Park and worked in a small firm handling DUI and traffic cases. He opened the McLane Law Firm in April 2011 and has built his firm on a strong referral base and solid reputation.


Jason HarveyReply

Posted Aug 16, 2023 at 23:00:41

Great Post! It’s important to note that detecting marijuana impairment is more challenging than detecting alcohol impairment due to the complexities of how THC affects individuals differently. This has led to ongoing discussions and debates about the accuracy and reliability of various testing methods, I recommend checking with legal sources or law enforcement agencies in your area.

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McLane Law Firm

Matt McLane has been defending individuals charged with DUI, traffic and criminal offenses since his graduation from Washburn University Law School in 1996. Licensed in the states of Kansas and Missouri. Mr. McLane specializes in DUI and criminal defense throughout the Kansas City metropolitan area.

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