Marijuana DUI in Flagstaff Arizona: Legal to Use, Still Illegal to Drive High

By Joe Styler, Editor — not an attorney · Sources checked July 30, 2026

Arizona legalized recreational marijuana in 2020, and a lot of people came away with the reasonable-sounding belief that a little weed and a drive is now like a beer and a drive — technically regulated, rarely charged. That belief is wrong, and it’s an expensive kind of wrong. Marijuana DUI is charged under the same statute as alcohol DUI in Flagstaff, carries the same mandatory jail and license penalties, and comes with a scientific wrinkle — how long marijuana stays in your body — that cuts both ways in the courtroom. Here’s what the law actually says.

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Two ways Arizona can charge a marijuana DUI

Arizona’s DUI statute reaches marijuana through two separate doors:

• Impairment (§ 28-1381(A)(1)). It’s a DUI to drive while impaired to the slightest degree by any drug — including marijuana. This is the door prosecutors mainly use now, and it doesn’t depend on a number; it depends on whether the state can show the marijuana actually affected your driving.
• The drug-or-metabolite clause (§ 28-1381(A)(3)). It’s also a DUI to drive with a proscribed drug “or its metabolite” in your body. On its face that sounds like zero tolerance — but Arizona’s Supreme Court significantly narrowed it, which is the single most important thing to understand about these cases.

The metabolite rule after State v. Harris

Marijuana leaves two kinds of traces in your body. One, Hydroxy-THC, is active and can actually impair you. The other, Carboxy-THC, is an inactive byproduct that does nothing to your driving — but lingers for 28 to 30 days after use. A blood test can flag Carboxy-THC weeks after a weekend that had nothing to do with the day you were pulled over.

In State ex rel. Montgomery v. Harris (2014), the Arizona Supreme Court held that the “metabolite” clause reaches only metabolites capable of causing impairment. In plain terms: you cannot be convicted under § 28-1381(A)(3) based only on inactive Carboxy-THC. Prosecuting someone for a metabolite that can’t impair them — and that can show up a month later — isn’t what the statute means. This ruling is the backbone of a lot of marijuana-DUI defenses, and it’s why the blood science in your specific case matters so much.

Note what Harris did not do: it didn’t legalize driving high. Active THC and actual impairment can still support a DUI. It simply closed the door on convicting sober people for month-old inactive traces.

There is no legal THC “limit” in Arizona

Unlike some states that set a per se number (for example, 5 nanograms of active THC), Arizona has no numerical marijuana limit. That cuts both ways. There’s no bright line you’re safe under — any amount plus impairment can be charged — but there’s also no automatic “over the limit” the way a 0.08 works for alcohol. Marijuana cases turn on impairment evidence and blood interpretation, not a single tidy number, which makes them more contestable and more dependent on how the state’s evidence was gathered.

A medical card is not a defense

Arizona’s medical-marijuana program protects your right to possess and use — it does not give you a pass to drive impaired. A valid card, and even lawful recreational use under Proposition 207, does not immunize you from a DUI if the state can show impairment. What legalization changed is possession law and the odor-alone stop rules; it did not change the impaired-driving statute.

How marijuana DUIs are actually fought

Because there’s no magic number, these cases live or die on the evidence of impairment and the blood science:

• Was it active THC or just Carboxy-THC? Under Harris, an inactive-metabolite-only case is vulnerable. The lab breakdown matters.
• The Drug Recognition Expert (DRE) evaluation. Officers use a 12-step DRE protocol to claim drug impairment; it has real reliability weaknesses that cross-examination can expose.
• Timing. When you last used versus when you drove is central — regular users can carry inactive traces long after any effect is gone.
• The blood draw itself. Warrant, chain of custody, storage, and the lab’s procedures all have to hold, same as in an alcohol case.

If your stop also involved a possession question — how much you had, odor-based searches, or edibles — our Flagstaff drug-crimes guide covers the possession side, and the main DUI guide covers the penalty framework these charges share.

Frequently asked questions

Marijuana is legal now — how can I get a DUI for it?

Legalization changed possession, not impaired driving. A.R.S. § 28-1381 still makes it a DUI to drive impaired to the slightest degree by marijuana, and the penalties are the same as an alcohol DUI — mandatory jail, fine, and a 90-day license suspension on a first offense.

Can I be charged just because THC showed up in my blood?

Not for an inactive metabolite alone. Under State v. Harris (Arizona Supreme Court, 2014), the presence of non-impairing Carboxy-THC — which can linger a month after use — cannot by itself support a § 28-1381(A)(3) conviction. Active THC or actual impairment is a different matter.

Does my medical marijuana card protect me?

It protects your right to use and possess; it does not protect impaired driving. A card is not a defense to a marijuana DUI if the state can show you were impaired.

Is there a legal THC limit I can stay under?

No. Arizona sets no numerical marijuana limit, so there’s no “safe” number — but there’s also no automatic per se violation the way 0.08 works for alcohol. These cases are decided on impairment evidence and blood interpretation.

What if I was using edibles or a prescription too?

The same impairment analysis applies, and mixing substances can complicate both the science and the defense. It’s exactly the kind of case where getting the blood evidence reviewed early matters.

I use marijuana daily for medical reasons — am I always at risk?

Daily users carry inactive Carboxy-THC traces continuously, which is exactly the situation Harris addresses: inactive metabolite alone can’t sustain a metabolite-clause conviction. But you can still be charged under the impairment clause if the state shows you were actually affected while driving. The practical takeaway for regular medical users is that the fight usually centers on active THC and real impairment evidence, not the mere fact that something showed up — which is why the blood breakdown and the officer’s observations matter so much.

Can secondhand smoke or a passenger’s use put THC in my blood?

Meaningful blood levels from purely passive exposure are generally not what these cases turn on, but the broader point holds: the source, timing, and type of THC in your blood are all fair game for a defense. If the state’s case leans on an ambiguous or low reading, how that number got there is worth scrutinizing with counsel.

Charged with a marijuana DUI in Flagstaff? Get a local read — free

Tell us what happened and whether blood was drawn, and we’ll connect you with an independent licensed Arizona attorney who handles marijuana-DUI cases in Coconino County. Free, confidential, no obligation.

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• Underage DUI & MIP (NAU students)
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• Flagstaff drug crimes — possession, and the odor-alone rules
• Flagstaff criminal defense overview