Marijuana Metabolites and DUI

In Arizona, it had long been assumed that "any" metabolite of an illegal drug in one's body satisfied the requirements of Arizona's Drug DUI statute, A.R.S. § 28-1381(A)(3).  This interpretation of the statute, however, lead to nonsensical results in that a person could legally smoke marijuana in any number of states which have legalized recreational use of marijuana, and weeks later no longer be under its influence, yet still be charged with DUI in Arizona. 

The Arizona Supreme Court took up this issue in State ex rel. Montgomery v. Harris (Shilgevorkyan), 237 Ariz. 98, 346 P.3d 984 (2014) and as of April 22, 2014, Motorists who have used marijuana can no longer be charged with driving under the influence simply because they had some non-active traces of the drug detected in their blood.  In State ex rel. Montgomery v. Harris (Shilgevorkyan), the Arizona Supreme Court provided clarity on Arizona's drug DUI statute, and what it means to be driving with a proscribed drug “or its metabolite” in one's body.  Prior to Harris, prosecutors interpreted the term "metabolite" to include any byproduct of a drug.  In a blunt rebuke to prosecutors, the court found that the State's interpretation that “its metabolite” includes any byproduct of a drug listed in § 13–3401 to lead to absurd results. Harris, 237 Ariz. 98, 102, ¶ 14, 346 P.3d 984, 988 (2014).

The court noted that the prosecutor's interpretation would create criminal liability regardless of how long the metabolite remained in the driver's system or whether it has any impairing effect.  The prosecutors, to be sure, acknowledged that, under their reading of the statute, if a metabolite could be detected five years after ingesting a proscribed drug, a driver who tested positive for trace elements of a non-impairing substance could be prosecuted. Given the illogical consequences of the State's interpretation, the court looked to the legislative intent of the statue and differentiated between active or potentially impairing metabolites vs. non-impairing metabolites. 

The court held, "that the legislature intended to prohibit driving with any amount of an impairing substance resulting from a drug proscribed in § 13–3401 in the body. 

The court's ruling does not affect that law regarding driving under the influence of a drug or alcohol and being impaired to the slightest degree.  It has been, and still is the law that in Arizona, it is unlawful to drive under the influence of any drug that drug impairs you to the slightest degree. However, the effects of marijuana ingestion are not as clear and well known as the effects of alcohol.  Given the legalization of marijuana in various state jurisdictions, the effects of marijuana are now being studied in greater depth. Tetrahydrocannabinol (THC) is the main psychoactive component of marijuana. Current studies and experts suggest that it is very difficult to ascertain how THC affects each person as an individual. Like alcohol consumption, some people can develop a tolerance for the affects of THC. It is also difficult to measure how much THC is being inhaled and/or ingested. With alcohol, a person knows how much alcohol is in a beer. For example, a 12 oz. light beer will have a distinct amount of alcohol in it. However, with marijuana, it is extremely difficult to measure the amount of THC in each plant. Different marijuana plants produce varying grades of THC. Further, human inhalations will vary from person to person. With all of these variables, it makes it extremely difficult to state whether a person is impaired simply looking at the amount of THC that was found in their blood. Some people with high concentrations of THC in the blood may have a tolerance to the effects of the THC and therefore, not feel the effects like someone who may be using it for the first time.

Links to websites and articles defining marijuana and THC:

https://en.wikipedia.org/wiki/Tetrahydrocannabinol

https://www.leafscience.com/2017/11/09/what-is-thc-tetrahydrocannabinol/

https://www.livescience.com/24553-what-is-thc.html

https://www.drugs.com/illicit/cannabis.html

Links to articles and studies regarding the effects of THC on driving:

https://www.nhtsa.gov/behavioral-research/drug-and-alcohol-crash-risk-study

https://www.nhtsa.gov/sites/nhtsa.dot.gov/files/documents/812355_drugalcoholcrashrisk.pdf

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4723241/

http://clinchem.aaccjnls.org/content/clinchem/61/10/1223.full.pdf