Understanding Marijuana DUIs in Arizona
What You Need to Know if You're Facing Charges in Tucson or Pima County
As marijuana becomes more socially accepted and legally accessible, many people assume that using it is risk-free—including when it comes to driving. But in Arizona, marijuana use can still lead to criminal charges if you're suspected of driving under the influence. If you're facing a marijuana DUI in Tucson or Pima County, it's important to understand how Arizona law treats these cases and why defending against them requires a unique legal strategy.
Unlike alcohol-related DUIs, marijuana DUIs are not based on a clear, measurable standard of impairment. There's no .08 equivalent for THC (the psychoactive compound in marijuana). Instead, the prosecution must prove that you were impaired "to the slightest degree" while in actual physical control of a vehicle, or that THC or its metabolites were present in your system while driving.
Here's the problem: science doesn't support the idea that the presence of THC in your system proves you're impaired. THC behaves very differently from alcohol. It's fat-soluble, meaning it's stored in the body for much longer periods, especially in regular users. A person can test positive for THC days or even weeks after use, long after any effects have worn off. This scientific reality has significant legal implications in DUI marijuana cases.
Multiple studies have confirmed that THC levels in the blood do not reliably correlate with driving impairment. A 2022 study published in Scientific Reports found that single measurements of THC in blood or breath are not reliable indicators of impairment. Similarly, research from the Lambert Initiative at the University of Sydney concluded that blood and saliva THC levels are weakly associated with actual impairment, particularly among frequent users. These findings are critical for anyone charged with a marijuana DUI in Pima County, where prosecutors often rely on chemical tests as primary evidence.
Even field sobriety tests (FSTs), which law enforcement officers routinely use during traffic stops, are not validated for detecting marijuana impairment. According to a study funded by the National Institute of Justice, officers frequently judged unimpaired participants as impaired based on FST performance. The American Bar Association has echoed these concerns, noting that FSTs and drug recognition evaluations may provide clues but do not offer conclusive proof of THC impairment.
In Tucson and throughout Arizona, marijuana DUIs are typically charged under Arizona Revised Statutes § 28-1381(A)(1) (driving while impaired to the slightest degree) and § 28-1381(A)(3) (driving with a drug or its metabolite in the body). Notably, the marijuana DUI laws do not include a "within two hours of driving" presumption like alcohol-based DUIs do. This legal distinction means the prosecution must connect your impairment to the time you were actually in control of the vehicle—a much more difficult task, especially when only THC metabolites are present.
In Pima County, law enforcement and prosecutors are increasingly aware of the scientific limitations in proving marijuana impairment, but many charges are still filed based on outdated assumptions about THC. If you were arrested for DUI marijuana in Tucson, especially if there was no erratic driving or no signs of impairment visible to the average observer, you may have a strong defense. For example, if you were parked in a lot or pulled over safely and admitted to recent use, that alone is not enough to convict you.
It's also important to understand that marijuana affects everyone differently. For regular users, particularly medical marijuana patients, the body develops tolerance. This means the presence of THC in the system has a reduced or negligible effect on motor skills or decision-making. The law doesn’t currently account for these differences, but juries do. In many cases, jurors are skeptical of the idea that a person was impaired simply because they tested positive for THC.
From a defense standpoint, one of the strongest arguments in a marijuana DUI case is that there is no reliable, scientific basis to equate THC presence with impairment. Prosecutors must prove actual impairment beyond a reasonable doubt—not just the presence of a substance. A skilled DUI attorney in Tucson will challenge the admissibility and reliability of the chemical test, the officer’s observations, and any FST results.
In some cases, the best resolution may be a plea to a reduced charge like reckless driving. This still carries consequences—including classes, fines, and a Victim Impact Panel—but it avoids jail time and the stigma of a DUI conviction. For individuals who were not driving dangerously and who do not present a threat to public safety, this is often a more just and proportionate outcome.
If you’re charged with DUI marijuana in Tucson or Pima County, don't assume you have to plead guilty. The science is on your side, and the law requires more than a positive THC test. An experienced criminal defense attorney can evaluate the evidence, explain your rights, and fight for a result that reflects the realities of marijuana science and Arizona law.
Sources and Supporting Research
Indeterminacy of cannabis impairment and ∆9-tetrahydrocannabinol (∆9-THC) levels in blood and breath
THC in blood and saliva are poor measures of cannabis impairment
Study finds driving impairment was not correlated with blood THC
Field Sobriety Tests and THC Levels Unreliable Indicators of Marijuana Intoxication
If you need help with a marijuana DUI in Tucson or anywhere in Pima County, AJB Law Firm is here to help. We know the law. We know the science. And we know how to fight for you.
