Last verified: April 2026
The Statute: Iowa Code §321J.2
Iowa Code §321J.2(1) makes it a crime to operate a motor vehicle:
- (a) While under the influence of an alcoholic beverage or other drug, or a combination;
- (b) While having an alcohol concentration of 0.08 or more;
- (c) While any amount of a controlled substance is present in the person, as measured in the person’s blood or urine.
Subsection (c) is the zero-tolerance per se rule — and it is the harshest interpretation of any drug-DUI law in the country. Unlike the alcohol provision, which relies on a quantitative threshold, the controlled-substance provision relies on detectability alone.
Iowa Code §321J.2(1)(c) makes it a crime to operate a motor vehicle while any amount of a controlled substance is present in the person, as measured in the person's blood or urine. The Iowa Supreme Court has repeatedly affirmed that "any amount" includes non-impairing metabolites like THC-COOH that can persist for 30+ days after last cannabis use.
Iowa Code §321J.2
The Comried – Childs Line of Cases
In State v. Comried, 693 N.W.2d 773 (Iowa 2005), the Iowa Supreme Court held that §321J.2(1)(c)’s “any amount” language means any detectable amount greater than zero, regardless of whether the driver was actually impaired. The court relied in part on early Arizona case law that Arizona itself later narrowed; the Iowa Supreme Court in State v. Childs, 898 N.W.2d 177 (Iowa 2017), expressly declined to follow Arizona’s narrowing approach.
In Childs, the defendant tested positive for the non-impairing carboxy-THC metabolite at 62 ng/mL in urine after admitting smoking half a joint earlier. The Iowa Supreme Court affirmed his OWI conviction, holding that Iowa’s “any amount” rule applies to non-impairing metabolites as well as active THC. As Iowa OWI defense lawyers describe it: “any amount means any amount greater than zero.”
In State v. Newton (2019), the court considered a due-process challenge to §321J.2(1)(c) on the grounds that THC–COOH metabolites can persist for 30+ days after impairment dissipates — meaning a driver can be convicted of OWI weeks after last consuming cannabis. The court found the statute constitutional.
THC–COOH Persistence in Urine
The carboxy-THC metabolite (THC–COOH) can be detected in urine for 3 to 30+ days after last cannabis use, depending on frequency, dose, and individual physiology. Heavy daily users can test positive for 60+ days. Active THC (Δ&sup9;-THC) in blood typically dissipates within 6–24 hours. Iowa’s per se rule applies to either compound, in either blood or urine.
Cross-River Return-Trip Exposure
The persistence rule has a stark practical consequence for Iowans who travel to legal-cannabis states. An Iowan who buys legal cannabis at a Rock Island, Illinois dispensary on Saturday and is pulled over for a routine traffic stop on Sunday faces criminal exposure under §321J.2(1)(c) for legal-elsewhere consumption. The federal interstate-transport prohibition (21 U.S.C. §841) makes carrying the product home a separate federal felony, but even disposing of the product before recrossing the river does not eliminate the OWI risk — the metabolite remains detectable. See cross-river return-trip exposure for more.
Implied Consent: Iowa Code §321J.6
A driver lawfully arrested on probable cause for OWI is deemed to have consented to chemical testing under Iowa Code §321J.6. Refusal to submit triggers automatic license revocation:
- One year for a first refusal
- Two years for a second or subsequent refusal
Refusal evidence is also admissible at trial.
The Drug Recognition Expert (DRE) Program
Iowa State Patrol and many local agencies maintain certified Drug Recognition Experts — officers trained in a 12-step physical and physiological evaluation protocol designed to identify impairment by drugs. The Des Moines Police Department, for example, operates with multiple DRE-certified officers who are dispatched to support OWI investigations. DRE testimony is admissible in Iowa courts and can support an impairment-based prosecution under §321J.2(1)(a) even in the absence of a controlled-substance test result.
Penalties Under Iowa Code §321J.2(2)
| Offense | Class | Jail | Fine | License Revocation |
|---|---|---|---|---|
| 1st offense | Serious misdemeanor | 48 hours min., up to 1 year | $1,000–$1,250 | 180 days |
| 2nd offense | Aggravated misdemeanor | 7 days min., up to 2 years | $1,875–$6,250 | 1 year (with interlock) |
| 3rd or subsequent | Class D felony | 30 days min., up to 5 years | $3,125–$9,375 | 6 years |
Source: Iowa Code §321J.2(2). Ignition interlock device required for any temporary restricted license; substance use disorder evaluation and Drinking Driver Course typically required.
The Narrow Affirmative Defense: §321J.2(7)
A patient operating under a controlled-substance prescription has an affirmative defense if (a) the substance was lawfully prescribed and dispensed, (b) taken in accordance with directions, (c) no alcohol was consumed, and (d) the practitioner had not directed the patient to refrain from operating a motor vehicle.
Per State v. Middlekauff, 974 N.W.2d 781 (Iowa 2022), an out-of-state medical marijuana card is not a "valid prescription" under Iowa law. Whether an Iowa medical cannabidiol registration card constitutes a "valid prescription" under §321J.2(7) remains unsettled, since the Iowa Supreme Court in Middlekauff held that no prescription for a Schedule I controlled substance can be "valid" because of marijuana’s federal scheduling. Iowa medical cannabidiol patients who consume THC and then drive remain at substantial OWI risk under the zero-tolerance per se rule, with the §321J.2(7) defense offering uncertain protection.
Practical Implications
The combined effect of the per se rule, metabolite persistence, the narrow affirmative defense, and Middlekauff is that Iowa law makes it functionally unsafe to drive in Iowa for at least 24–48 hours after last cannabis use, with longer windows for frequent users. Out-of-state cardholders cannot drive in Iowa with detectable metabolites at all. And the Childs “any amount” rule means a routine traffic stop, leading to a probable-cause OWI arrest and a urine test, can produce a conviction even when the driver was not impaired in any conventional sense.
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