Drug DUI in Arizona works differently than alcohol DUI in one crucial way. There’s no 0.08-style number to measure against. Instead, the law looks at whether a proscribed drug or its metabolite was in the driver’s body at all. That single difference has produced some of the most contested DUI litigation in the state.
The statute behind drug DUI in Arizona
Under A.R.S. § 28-1381(A)(3), it’s illegal to drive or be in actual physical control of a vehicle while there’s any drug listed in A.R.S. § 13-3401, or its metabolite, in the driver’s body. That list covers marijuana and its derivatives along with a range of controlled substances. Unlike the alcohol statutes, this provision doesn’t require the state to prove impairment. It only requires proof the substance or its metabolite was present.
Why “any drug metabolite” makes drug DUI different
A metabolite is what’s left after the body breaks a substance down. For marijuana specifically, THC metabolizes into Hydroxy-THC first, which is capable of causing impairment. Hydroxy-THC further breaks down into Carboxy-THC, which is not. Carboxy-THC can linger in a person’s system for weeks after use — long after any impairing effect has worn off.
The Arizona Supreme Court narrowed the metabolite rule
In State ex rel. Montgomery v. Harris, 210 Ariz. 288 (2014), the Arizona Supreme Court addressed a case where a driver tested positive only for Carboxy-THC, the non-impairing metabolite. The court held that the “metabolite” reference in § 28-1381(A)(3) is limited to metabolites capable of causing impairment. That means a driver can’t be convicted under this section based solely on a non-impairing metabolite like Carboxy-THC. The state has to show the substance found is capable of impairing a driver in the first place.
What this drug DUI ruling does and doesn’t change
The ruling narrowed the statute, but it didn’t eliminate the possibility of a sober-driving DUI charge entirely. A driver with only an active, impairing metabolite present can still be prosecuted under this section. That holds true even at a trace amount and even without evidence of actual impaired driving, because the statute doesn’t require proof of impairment — only presence of an impairing substance or metabolite. Prosecutors can also charge, separately, under Arizona’s general “impaired to the slightest degree” standard. That’s a different legal theory the Harris ruling doesn’t touch.
The medical marijuana exception
A.R.S. § 28-1381(D) provides that a person using a drug as prescribed by a licensed medical practitioner isn’t guilty of violating the metabolite provision. This can matter for registered medical marijuana patients. It doesn’t extend to the “impaired to the slightest degree” theory of DUI, though, which still applies regardless of whether the underlying use was legal.
Prescription medication and drug DUI
The statute isn’t limited to illegal drugs. Prescription medications that impair driving ability can also support a drug DUI charge. Having a valid prescription is not automatically a defense if the medication actually impaired the driver’s ability to operate a vehicle safely.
The bottom line
Drug DUI in Arizona hinges on the presence of a proscribed drug or an impairing metabolite, not a numeric threshold like alcohol DUI. The Harris ruling narrowed the metabolite provision to substances capable of causing impairment. Active metabolites and impaired-driving theories both remain very much in play, though. Whether a specific test result falls on one side of that line or the other is a scientific and legal question that depends on exactly what substance was found.
Frequently asked questions
No. A.R.S. § 28-1381(A)(3) only requires that a proscribed drug or an impairing metabolite was present in the driver’s body, not proof of actual impaired driving.
Under the Arizona Supreme Court’s ruling in the Harris case, a driver cannot be convicted based solely on a non-impairing metabolite like Carboxy-THC. The metabolite must be capable of causing impairment.
A.R.S. § 28-1381(D) provides an exception for drugs used as prescribed by a licensed practitioner, but it doesn’t extend to Arizona’s separate ‘impaired to the slightest degree’ standard.
Yes. A valid prescription doesn’t automatically prevent a charge if the medication actually impaired the driver’s ability to operate a vehicle safely.
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This article explains Arizona’s drug DUI statute and the Arizona Supreme Court’s ruling on metabolites. It is not a substitute for a toxicology or legal review of any specific test result, which depends on the exact substance identified.