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THC per se laws are not scientifically reliable

By John Buckley - May 17, 2016

Last week, the American Automobile Association (AAA) released a study that is in direct conflict with Colorado DUI laws where marijuana is concerned.  The study results found that drugged driving laws which create a per se limit for marijuana in the bloodstream are not scientifically valid.  The researchers reported that it isn’t possible to set a THC threshold which can allow a juror to reliably determine impairment.  “There is understandably a strong desire by both lawmakers and the public to create legal limits for marijuana impairment in the same manner we do alcohol,” said Marshall Doney, AAA’s president and CEO. “In the case of marijuana, this approach is flawed and not supported by scientific research.”  This isn’t the first such determination.  The National Highway Traffic and Safety Administration also found that “it is difficult to establish a relationship between a person's THC blood or plasma concentration and performance impairing effects.” 


Despite such scientific findings, Colorado passed a law in 2013 which states that “if at such time (when a defendant was operating a motor vehicle or found to be in actual physical control of a motor vehicle) the driver’s blood contained five nanograms (ng) or more of (THC) per milliliter of whole blood…such fact gives rise to a permissible inference that the defendant was under the influence of one or more drugs.”  The crucial language for the DUI defense attorney in such a case is the permissible inference.  A jury, deciding the fate of a driver accused of drugged driving, MAY infer that the defendant is impaired based on the blood test results.  However, that jury may also consider other evidence of a driver’s lack of impairment.  Lack of poor driving, lack of reliability of field sobriety testing, and video evidence can all be introduced in a DUI trial. 

Interestingly, Colorado had attempted to pass a marijuana DUI per se law for several years but those in favor of the bill could not convince the state legislature that the science was sound.  Cynthia Burbach, the then head of the Colorado Department of Public Health and Environment’s toxicology lab, testified that the 5 ng per se limit was more than fair.  Ms. Burbach has since resigned as the state’s chief toxicologist amid claims of bias and poor science in her lab.

If you have been charged with a DUI in Denver or elsewhere in Colorado, please consult with a DUI defense attorney to discuss your case before going to court.