State v. Harris: Why a Non-Impairing Marijuana Metabolite Can’t Support an Arizona DUI Charge

By Gordon Thompson, Phoenix DUI & Criminal Defense Attorney — 47 years of experience, 6,000+ cases. Page reviewed July 2026.

Quick answer: In State ex rel. Montgomery v. Harris, 234 Ariz. 343 (2014), the Arizona Supreme Court ruled that the phrase “its metabolite” in Arizona’s drug-DUI statute, A.R.S. § 28-1381(A)(3), only covers metabolites capable of causing impairment. Carboxy-THC — a common, non-impairing marijuana byproduct that can linger in the blood for up to a month — cannot by itself support a DUI charge under that section.

The Traffic Stop That Led to a Landmark Ruling

The case began with a routine traffic stop. Phoenix-area police pulled over Hrach Shilgevorkyan for speeding and unsafe lane changes. Suspecting impairment, officers ran field sobriety tests. Shilgevorkyan admitted he had smoked marijuana the night before and voluntarily agreed to a blood test. The results came back positive — not for active THC, and not for Hydroxy-THC (the metabolite capable of causing impairment), but for Carboxy-THC alone: an inactive breakdown product with no impairing effect.

The State charged him with two separate DUI counts: one under A.R.S. § 28-1381(A)(1), which requires proof of actual impairment “to the slightest degree,” and one under A.R.S. § 28-1381(A)(3), Arizona’s strict “per se” drug-DUI provision, which criminalizes driving with any proscribed drug — or its metabolite — in the body, regardless of impairment.

The Legal Question: What Does “Its Metabolite” Actually Mean?

The Arcadia Biltmore Justice Court dismissed the (A)(3) charge, and the Maricopa County Superior Court affirmed. The Court of Appeals reversed, siding with the State’s broad reading. The case then reached the Arizona Supreme Court, which had to answer a narrow but high-stakes question: does “its metabolite” in § 28-1381(A)(3) include every possible breakdown product of a proscribed drug, or only the ones that can actually impair a driver?

Marijuana breaks down into multiple metabolites. Hydroxy-THC forms first and can cause impairment, but it converts quickly into Carboxy-THC — which does not impair a driver and, according to expert testimony in the case, can remain detectable in blood for 28 to 30 days after use. Arizona’s crime lab routinely tests only for Carboxy-THC because Hydroxy-THC breaks down too fast to reliably capture.

The Court’s Holding: Metabolites Must Be Capable of Impairment

Writing for the majority, Justice Brutinel found the statutory language genuinely ambiguous — it could reasonably be read as singular or plural, and even in the plural it could plausibly mean only the primary, impairing metabolites of a given drug. Rather than adopt the State’s flat, zero-tolerance reading, the Court looked to legislative intent, statutory context, and the doctrine against absurd results.

The Court identified three reasons the State’s broad interpretation would produce absurd outcomes:

• No time limit on liability. Under the State’s reading, a driver could be prosecuted years after ingesting a drug, as long as any trace byproduct remained detectable — even with zero impairing effect at the time of driving.
• It would criminalize legal medical marijuana use. Because Carboxy-THC can linger for up to a month, an AMMA-compliant medical marijuana patient could face DUI prosecution for driving weeks after legally using their medicine, with no impairment whatsoever.
• It could sweep in unrelated legal substances. The Court noted that some legal substances share metabolites with proscribed drugs (for example, serotonin and the proscribed drug bufotenine both break down into 5-HIAA), meaning the State’s reading could theoretically support a charge with no illegal drug ever having been ingested.

Based on the statute’s placement within Arizona’s “Driving Under the Influence” statutory scheme, its legislative history, and its underlying purpose of preventing impaired driving — not punishing the mere presence of a harmless residue — the Court held: the “metabolite” reference in § 28-1381(A)(3) is limited to metabolites capable of causing impairment. Because Carboxy-THC does not cause impairment, it cannot support an (A)(3) charge standing alone.

The Dissent: A Different View of “Zero Tolerance”

Justice Timmer dissented, arguing the statutory language was not ambiguous at all and that the legislature intended a true zero-tolerance, per se rule — precisely because proving actual drug impairment is far harder than proving alcohol impairment via a breath test. The dissent noted that a flat ban makes enforcement more workable and pointed out that any unfair applications (such as against a legal medical marijuana user) could be challenged separately as unconstitutional “as applied,” rather than by reinterpreting the statute for everyone. This tension — between administrability and fairness to individual defendants — remains a live theme in drug-DUI litigation today.

What This Means for You

If you were arrested for a marijuana-related DUI in Phoenix, Scottsdale, Tempe, Mesa, Chandler, Gilbert, Glendale, Peoria, Surprise, Goodyear, Avondale, Buckeye, or anywhere else in Maricopa or Pinal County, State v. Harris directly affects your case in several ways:

• A Carboxy-THC-only blood result is not, by itself, enough to convict you under A.R.S. § 28-1381(A)(3). If the lab report in your case shows only Carboxy-THC and no active THC or Hydroxy-THC, that is a significant defense issue worth raising immediately.
• You can still be charged under A.R.S. § 28-1381(A)(1) if the State has other evidence — field sobriety tests, driving pattern, officer observations — suggesting impairment “to the slightest degree.” Harris does not eliminate that avenue for the State.
• Medical marijuana patients get added protection, but not immunity. A.R.S. § 28-1381(D) and the reasoning in Harris help AMMA cardholders, but prosecutors can still pursue an (A)(1) impairment charge.
• The lab report matters enormously. Whether the State tested for — and found — Hydroxy-THC versus only Carboxy-THC can be the difference between a viable case and a dismissible one.

These are fact-specific, technical distinctions that depend on your toxicology report, the officer’s report, and how the charges were filed. This article is general legal information, not legal advice for your specific situation.

Frequently Asked Questions

What did the Arizona Supreme Court decide in State v. Harris?

The Court held that the “metabolite” language in A.R.S. § 28-1381(A)(3) applies only to metabolites capable of causing impairment. Because Carboxy-THC does not cause impairment, its presence alone cannot support an (A)(3) DUI charge.

What is Carboxy-THC and why does it matter in a DUI case?

Carboxy-THC is an inactive, non-psychoactive byproduct created when the body breaks down THC. It does not cause impairment and can remain detectable in blood for roughly 28 to 30 days after marijuana use — long after any impairing effect has worn off.

Can I still be charged with DUI in Arizona for driving after using marijuana days earlier?

The State cannot rely solely on a non-impairing metabolite like Carboxy-THC to prove an (A)(3) charge. However, you can still be charged under A.R.S. § 28-1381(A)(1) if the State has other evidence you were impaired to the slightest degree, or under (A)(3) if active THC or an impairing metabolite is found.

Does having a medical marijuana card protect me from a DUI charge in Arizona?

A valid AMMA card provides some statutory protection under A.R.S. § 28-1381(D) against an (A)(3) charge, but it does not protect you from an (A)(1) charge if the State proves actual impairment. Each case turns on its specific facts.

What is the difference between an A.R.S. § 28-1381(A)(1) and (A)(3) DUI charge?

An (A)(1) charge requires proof you were impaired to the slightest degree while driving. An (A)(3) charge doesn’t require proof of impairment — only proof of a proscribed drug or its impairing metabolite in your body. Harris narrowed (A)(3) so it can’t rest on non-impairing metabolites alone.

Why did the dissenting justice disagree with the majority?

Justice Timmer argued the statute’s language wasn’t ambiguous and reflected a deliberate zero-tolerance rule, given how much harder drug impairment is to prove than alcohol impairment. She viewed unfair applications as better handled through individual “as applied” constitutional challenges.

How do police test for marijuana metabolites in a DUI case?

Blood tests can detect both Hydroxy-THC (impairing) and Carboxy-THC (non-impairing). Because Hydroxy-THC converts quickly into Carboxy-THC, Arizona’s crime lab typically reports only Carboxy-THC — the exact issue this case addressed.

Who should I call if I’m facing a marijuana-related DUI charge in Phoenix or Maricopa County?

Contact a DUI attorney experienced in Arizona drug DUI defense right away. Gordon Thompson, a Phoenix DUI and criminal defense attorney with 47 years of experience and 6,000+ cases, offers free consultations and can evaluate whether the metabolite evidence in your case still supports a charge under current Arizona law.

Case citation: State ex rel. Montgomery v. Harris, 234 Ariz. 343, 322 P.3d 160 (Ariz. 2014). This article is for general informational purposes only and does not constitute legal advice. Reading this article does not create an attorney-client relationship. For advice about your specific situation, contact Gordon Thompson for a free consultation.