Cannabis DUI Law in Arizona: A Review of Kaplan’s Navigating the Haze
This articles reviews Navigating the Haze: Arizona's Cannabis Legalization, Zero-Tolerance DUI Statutes, and the Need for Scientific Clarity by Rachel Kaplan, published in the Law Journal for Social Justice (2025; Free)
In her award winning article , Rachel Kaplan confronts one of the most pressing contradictions in cannabis law: Arizona’s legalization of recreational cannabis exists side-by-side with zero-tolerance DUI statutes that criminalize drivers for the mere presence of Cannabis metabolites.
For law firms, this tension creates a fertile ground for litigation. For policymakers, it underscores the urgent need for reform.
The Dilemma of Arizona’s DUI Law
Arizona’s DUI statute (A.R.S. § 28-1381(A)(3)) allows conviction if any trace of cannabinoid-like metabolites are found in a driver’s system—even without proof of impairment. This approach is vastly different from alcohol law, where a 0.08% BAC threshold has decades of scientific consensus behind it.
Kaplan captures the injustice clearly: “To punish a driver for ingesting cannabis hours or even days prior to driving a vehicle would, in essence, penalize his lawful act of consuming a legal substance.”
Cannabis vs. Alcohol: Science on Trial
Unlike alcohol, cannabis impairment currently lacks a clear, predictable metric. THC’s psychoactive effects last hours, but its metabolites remain detectable for days or weeks. Blood tests may confirm use, but they cannot confirm impairment.
As Kaplan notes, “The scientific uncertainty demonstrated through THC blood testing is different from the reliability of its predecessor, the measurement of alcohol impairment. The psychoactive effects of alcohol are predictable and uniform… at least to the extent that scientists universally agree that drivers who have reached the 0.08% threshold are impaired.”
This difference is critical for attorneys: juries often view toxicology reports as authoritative, yet the science behind cannabis testing is far less conclusive than alcohol.
Comparisons Beyond Arizona
Arizona is not alone in this dilemma:
Colorado and Washington have adopted per se limits of 5 ng/mL THC in blood. Yet research shows frequent cannabis users may exceed this level without impairment, while occasional users may be impaired below it.
Nevada previously enforced a per se THC limit but repealed it in 2021, recognizing the lack of scientific support. The state now relies on evidence of actual impairment, such as officer observations and field sobriety tests.
California has resisted adopting a THC per se limit, emphasizing behavioral evidence of impairment over toxicology alone.
Kaplan’s analysis places Arizona at the restrictive end of this spectrum. Its zero-tolerance approach exposes drivers to conviction even when no safety risk exists. This something courts, regulators, and defense attorneys must grapple with.
Real-World Implications
The stakes go beyond roadside stops. These same testing issues spill into employment law, workers’ compensation claims, and civil liability cases.
In my own work:
During a Department of Homeland Security training I conducted last year, which included modules on impairment detection technology, we examined the strengths and weaknesses of current tools. None could reliably prove impairment in real time.
Employment cases are very common when an employees fails a drug test after consuming a CBD or hemp product. These drug testing disputes arise due to smalls amounts of THC in some hemp products.
In my American Journal of Endocannabinoid Medicine article on DWIC, I emphasized the need for science-based approaches that distinguish lawful use from actual impairment.
And as I argued in my Rolling Stone essay, our fragmented, siloed data systems make it nearly impossible to draw firm conclusions about cannabis impairment—leaving courts and employers to rely on flawed assumptions.
For attorneys, this means challenging the state’s reliance on metabolite detection and questioning whether such evidence actually correlates with unsafe driving.
Pathways for Reform
Kaplan offers several reform options:
Reassessing zero-tolerance statutes that criminalize lawful use.
Favoring effect-based laws requiring proof of actual impairment.
Investing in research toward scientifically defensible standards.
Abolishing cannabis-specific DUI statutes in favor of laws targeting dangerous driving behavior.
For law firms, these proposals highlight potential areas of constitutional challenge, evidentiary disputes, and expert testimony.
Conclusion
Kaplan’s Navigating the Haze should be essential reading for attorneys and regulators confronting cannabis DUI cases. It shows how Arizona’s current statutes risk criminalizing lawful behavior while failing to ensure road safety. For attorneys preparing defenses, and for regulators considering reforms, the lesson is clear: without scientific clarity, DUI law risks collapsing under its own contradictions. Especially, when we consider the number of possible court challenges from exposure to trace amounts of THC in hemp products.
For law firms handling cannabis-related DUI or impairment cases, expert testimony can be critical. The science is unsettled, the law is evolving, and juries often need guidance to separate presence from impairment.
