The Tricky Case of Drugged (Cannabis) Driving

As states continue slowly shuffling towards cannabis legalization, dozens of different types of statutes may need to be re-examined in light of marijuana’s changed status. Chief among them are state driving under the influence of drugs (DUID) laws. Since legislatures are often slow to act (or in some cases have deliberately chosen not to address the issue, as in Colorado), it may be up to state courts to make necessary adjustments to DUI law.

The Arizona Supreme Court recently did just that in a case examining whether the presence of non-impairing carboxy-THC* in a person’s system was enough to convict him for driving under the influence of marijuana. Defendant Hrach Shilgevorkyan was stopped for suspected impaired driving after having smoked marijuana the night before, but blood tests revealed only the presence of carboxy-THC, not hydroxy-THC, the hallucinogenic compound found in marijuana. On this basis, Shilgevorkyan asked the court to throw out the charge against him for driving a vehicle “[w]hile there is any drug … or its metabolite in the person’s body.” Shigevorkyan argued that to punish him for having a non-impairing metabolite (carboxy-THC) in his system would be inconsistent with the Arizona legislature’s intent to criminalize driving under the influence. The trial court agreed, but the state won a later appeal relying on prior precedents that had held the term “metabolite” was not over inclusive,  unconstitutionally vague, or overbroad.

The Arizona Supreme Court, however, sided with Shilgevorkyan, holding that the “its metabolite” language was open to multiple interpretations, rendering it ambiguous. Thus, the court turned to legislative intent in construing the statute. Noting that the legislative purpose behind the statute was to prevent impaired driving, the court determined that accepting the state’s position would lead to an absurd result — criminalizing non-impairment. The court further expressed concern that the otherwise lawful conduct of medical marijuana patients would be criminalized under the broader reading of the statute. Rejecting these potential outcomes, the court ruled that “its metabolite” must refer only to metabolites with the potential to impair driving. In other words, not carboxy-THC.

State DUI law varies widely, but this case has implications for many that already have, or are contemplating, legalizing marijuana in some form. For example, in Illinois, which has a zero tolerance stance towards DUID (625 ICS §5/11-501(a)(6) penalizes “any amount” of a drug, substance, or compound from the unlawful use or consumption of cannabis), this case may provide a sound, logical interpretation to the intersection of the zero tolerance law and further provisions exempting qualified patients from criminal liability. Washington’s recently-revised DUID statutes (RCW 46.61.502(1)(b)) set a limit to THC concentration (less than 5 nano grams per milliliter), much like blood alcohol levels, but fails to distinguish between the impairing and non-impairing THC metabolites. The Shilgevorkyan case underscores the need to recognize the difference. New York, currently debating its own medical marijuana legislation, has a straightforward prohibition on impaired driving (Vehicle and Traffic Law § 1192(4)), but if the legislature is not clear about how to test for impairment (e.g., THC level, hydroxy-THC level?), that simple statute could be subject to strained interpretations.

Revising DUID statutes seems to be low-priority for many legislatures, even those considering drastic revisions to their marijuana laws. Until they start taking the issue head-on, we should be grateful for sound opinions, like that of the Arizona Supreme Court in Shilgevorkyan.


* Carboxy-THC can remain in a person’s body for approximately one month after marijuana use or ingestion. The intoxicating hydroxy-THC compound begins to break down after just a few hours.