Arizona Drug DUI Defense: Who Has to Prove Your Prescription Was Valid?

What Happened in State v. Bayardi?

The defendant, Joseph Fannin, was charged in Phoenix Municipal Court with two counts of DUI: one for driving impaired to the slightest degree, and a second count under A.R.S. § 28-1381(A)(3) for driving with an “impermissible drug” — in his case, Methadone, Klonopin, and Ritalin — in his system. Arizona’s drug DUI law doesn’t require the State to prove actual impairment for this type of charge; simply having a prohibited drug or its metabolite in your body while driving is enough.

Fannin argued he was taking all three medications exactly as prescribed. The fight wasn’t over whether he had valid prescriptions — it was over who has to prove what to the jury, and how convincingly.

The Legal Question: Who Carries the Burden?

Fannin wanted the jury instructed that the State had to prove, beyond a reasonable doubt, that he was not using the drugs as prescribed. The City of Phoenix prosecutor argued the opposite: that Fannin had to prove, by a lower “preponderance of the evidence” standard, that he was using them as prescribed. The municipal court sided with Fannin at first; the superior court reversed and sided with the State. Fannin then appealed.

Why does this distinction matter so much?

Arizona criminal law recognizes three categories of defenses, and each shifts the burden of proof differently:

• Defenses that deny an element or responsibility (like alibi) — the State always keeps the burden of proving guilt beyond a reasonable doubt.
• Justification defenses (like self-defense or necessity) — once raised, the State must disprove them beyond a reasonable doubt.
• Affirmative defenses — the defendant must prove them, but only by a preponderance of the evidence (more likely than not).

Which bucket the prescription-drug exception falls into decides whether the defendant or the prosecutor has the harder job at trial.

How Did the Court Rule, and Why?

The Court of Appeals held that A.R.S. § 28-1381(D) is an affirmative defense. The reasoning came down to three points:

It doesn’t deny an element of the charge

Fannin didn’t argue the prescription-drug exception was actually part of what the State has to prove to win a conviction. Since it doesn’t negate an element of the A.R.S. § 28-1381(A)(3) charge itself, it isn’t an “element-denying” defense.

It isn’t a justification defense

Arizona law limits true justification defenses to Chapter 4 of the Criminal Code — things like duress, necessity, and use of force. Those defenses don’t even apply to Title 28 traffic offenses like DUI in the first place. The court also rejected the argument that the “is not guilty” language in § 28-1381(D) signaled a justification defense, noting that every successful defense — of any type — results in a “not guilty” verdict. That phrase describes the outcome, not the category.

By elimination, it’s an affirmative defense — and the statute’s structure confirms it

Since it’s neither of the first two categories, Arizona’s Criminal Code says it must be an affirmative defense. The court also pointed out that § 28-1381(D) appears as a separate exception in a different subsection than the underlying charge — and under long-standing Arizona precedent, a defendant relying on an exception written into a distinct clause bears the burden of showing they qualify for it.

Does This Ruling Apply to All Drug DUI Cases in Arizona?

Yes — this case is the controlling appellate authority on this exact question statewide, and the court noted the issue hadn’t been resolved in any prior published Arizona decision. It applies specifically to drug DUI charges under A.R.S. § 28-1381(A)(3) where the defense is that the drug was taken as prescribed by a licensed medical practitioner (physician, dentist, podiatrist, or osteopath).

What This Means for You

If you’ve been arrested for DUI in Maricopa County, Pinal County, or elsewhere in Arizona, and a blood or urine test came back positive for a prescription medication — not an illegal drug — State v. Bayardi is directly relevant to your case in a few concrete ways:

• The burden is on you, not the prosecutor. You cannot simply argue “the State can’t prove I abused it.” You need to affirmatively show you had a valid, current prescription and were taking the medication as directed.
• Documentation is everything. Pharmacy records, prescription bottles, and communication with your prescribing doctor can be the difference between a conviction and a dismissal.
• This is a preponderance standard, not proof beyond a reasonable doubt. That’s a lower bar than what the State faces on the underlying charge — which is actually good news, but it still requires real evidence, not just your word.
• An experienced DUI attorney can identify whether this defense even applies — and whether other defenses (like unlawful stop or testing procedure issues) may be stronger in your particular case. Read more about DUI defense strategies in Arizona and the penalties you could be facing if convicted.

Frequently Asked Questions

What is State v. Bayardi about?

It’s a 2012 Arizona Court of Appeals ruling holding that the prescription-drug exception in A.R.S. § 28-1381(D) is an affirmative defense — meaning the defendant, not the State, must prove by a preponderance of the evidence that they were using the drug as prescribed.

Does the State have to prove I abused my prescription?

No. The State only needs to prove the prohibited drug or its metabolite was in your body while you were driving. You carry the burden of proving valid prescription use as a defense.

What’s the difference between an affirmative defense and a justification defense in Arizona?

A justification defense (like self-defense) means the conduct was never criminal — once raised, the State must disprove it beyond a reasonable doubt. An affirmative defense excuses otherwise-criminal conduct, and the defendant must prove it by the lower preponderance-of-the-evidence standard. Bayardi held the prescription-drug exception falls into the second category.

Can I still be charged with DUI if I was taking medication exactly as prescribed?

Yes, you can still be charged. A.R.S. § 28-1381(D) gives you a defense, but under Bayardi, you have to prove you qualify for it — the charge itself doesn’t go away automatically just because you have a prescription.

Which medications can trigger a drug DUI charge in Arizona?

Any substance listed under A.R.S. § 13-3401 — including many common opioids, benzodiazepines (like Klonopin), and stimulants (like Ritalin) — can support a drug DUI charge under A.R.S. § 28-1381(A)(3) if it or its metabolite is found in your system while driving, regardless of whether you were actually impaired.