Do Breathalyzers Detect Weed? Arizona THC Testing, ARS 28-1381

No. The breath testing devices Arizona police use, both the handheld preliminary screens at the roadside and the evidentiary Intoxilyzer at the station, are built to measure ethanol. They cannot detect THC or any other drug. A driver who has used marijuana and no alcohol will blow a 0.00, and officers know it. That is why a marijuana DUI stop in Arizona does not end at the breath test. It moves to a different set of tools, and in nearly every case to a blood draw.

People ask this question for two reasons. Some are worried that an interlock device or a workplace breath test will flag cannabis; it will not. Others have just been arrested, blew clean, and want to know how the State can still charge them. This article answers the second question, which is where the real risk lies under A.R.S. § 28-1381. Our Arizona drug DUI defense page covers the charge itself.

Why Can’t a Breath Test Find THC?

Because of chemistry. Alcohol is a small, volatile molecule that moves from the blood into the air in the lungs in a predictable ratio, which is what a breath device measures. THC is a large, fat-soluble molecule that is carried in the blood and stored in body fat; it does not pass into exhaled breath in amounts a breath device can read. The Intoxilyzer measures how much infrared light ethanol absorbs in a breath sample, and THC does not absorb at those wavelengths at all. The handheld screens use a fuel cell that reacts to ethanol specifically.

Devices that claim to detect THC in breath exist as research and pilot products, but none is in evidentiary use in Arizona courts, and no Arizona statute sets a breath standard for marijuana. The chemical test the State relies on in a marijuana case is blood.

What Does Arizona Use Instead of a Breathalyzer?

Four things, in sequence. First, the officer’s observations: the driving that prompted the stop, the smell of burnt or raw marijuana, red or glassy eyes, slowed responses and anything you say about recent use. Second, the standardized field sobriety tests, the walk-and-turn, one-leg stand and horizontal gaze nystagmus, which were designed for alcohol and are used anyway. Third, if the officer suspects drugs, a Drug Recognition Expert may be called to run a twelve-step evaluation that includes pulse, blood pressure, pupil measurement in a dark room and a test for lack of eye convergence. Fourth, a blood draw under Arizona’s implied consent law.

Our companion article explains each step in detail: how police test for weed in an Arizona DUI. The point for this question is that none of those steps involves a breath device, and a 0.00 breath result is often the moment the officer decides to pursue a drug case.

What Does the Blood Test Actually Show?

The lab reports three compounds, each in nanograms per milliliter. Delta-9 THC is the active drug. 11-hydroxy-THC is the active metabolite the body makes as it processes THC. Carboxy-THC is the inactive metabolite that remains in the body for days or weeks after use. The distinction matters because the Arizona Supreme Court held in State ex rel. Montgomery v. Harris (2014) that the drug-in-body charge under § 28-1381(A)(3) cannot rest on carboxy-THC alone, since that metabolite cannot cause impairment. A blood test showing only carboxy-THC supports no (A)(3) charge.

The blood must be drawn by a physician, a registered nurse or another qualified person under A.R.S. § 28-1388, and the sample then travels to a crime lab for analysis. The time between the stop and the draw, the storage of the vial, the calibration of the instrument and the lab’s own uncertainty figures are all part of the defense in a THC case. Our post on breath versus blood tests in Arizona explains why blood cases are fought differently.

Can You Refuse the Blood Test in Arizona?

You can refuse, but refusing has its own consequences and rarely stops the draw. Under A.R.S. § 28-1321, every driver in Arizona has given implied consent to a test of blood, breath, urine or other bodily substance after a DUI arrest. A refusal triggers a license suspension through the MVD that is separate from the criminal case, and officers in Maricopa County routinely obtain a telephonic search warrant for blood within minutes of a refusal. Our article on refusing a breathalyzer in Arizona walks through the suspension and the warrant process; the same rules apply to a blood request.

What Charge Follows a Positive THC Blood Test?

Two, usually. The impairment charge under § 28-1381(A)(1) alleges you were impaired to the slightest degree by a drug, and it is proven with observations, the field tests and the DRE evaluation. The drug-in-body charge under § 28-1381(A)(3) alleges that THC or its active metabolite was in your body while you drove, but under A.R.S. 36-2852(B) a person is guilty of it only if also impaired to the slightest degree. Both are class 1 misdemeanors for a first offense, carrying at least ten consecutive days in jail and a fine of at least $250 plus assessments under § 28-1381(I). What a first conviction looks like in practice is covered in our guide to a first drug DUI in Arizona.

How Tamou Law Group Defends a Marijuana DUI After a Clean Breath Test

Pre-charge advocacy. A blood result takes weeks to come back, and the charge is often not filed until it does. We use that window to preserve the body-camera footage, the dispatch timeline and the warrant paperwork, and to get the lab’s full data package rather than the one-page summary. Our Phoenix DUI lawyers start that work the day you call.

Disclosure strategy. We demand the chromatograms, calibration records, uncertainty budget and chain-of-custody log for the blood sample, the DRE’s face sheet and rolling log, and the officer’s SFST training records. A THC case is lost by the State in those documents far more often than at the roadside.

Plea and collateral analysis. If the (A)(3) count rests on carboxy-THC, we move to dismiss it under Harris. If you hold a medical marijuana card, we build the affirmative defense the Supreme Court recognized in Dobson v. McClennen. Where a plea is the right outcome, we negotiate it with the suppression motion and the toxicology report on the table, and we explain the MVD, interlock and record consequences before anything is signed. See how we approach beating a marijuana DUI in Arizona.